FetchEvent.clientId

The clientId read-only property of the FetchEvent interface returns the id of the Client that the current service worker is controlling.

The Clients.get() method could then be passed this ID to retrieve the associated client.

var myClientId = fetchEvent.clientId;

A DOMString that represents the client ID.

self.addEventListener('fetch', function(event) {
  console.log(event.clientId);
});

• Using Service Workers
• Service workers basic code example
• Is ServiceWorker ready?
• Promise
• Using web workers