The registration read-only property of the BackgroundFetchEvent interface returns a BackgroundFetchRegistration object.

A BackgroundFetchRegistration.

In this example, if the user clicks on the user interface displaying the download progress, this fires the onbackgroundfetchclick event. The current BackgroundFetchRegistration is returned by calling event.registration.

addEventListener("backgroundfetchclick", (event) => {
  console.log(event.registration);
});