Extracting response body from service worker fetch event

Question

I'm trying to enable push notification on my react app (PWA).

This is my service worker file. I've successfully done so whenever a request is made to a specific endpoint by doing so

self.addEventListener('activate', function(event) {
  console.log('Claiming control');
  return self.clients.claim();
});

self.addEventListener('fetch', async event => {
  const url = new URL(event.request.url);
  //
  if (url.pathname === 'my-endpoint') {
    //I want the notification to display the response data
    event.waitUntil(
      self.registration.showNotification('custom title', {
        body: 'custom body'
      })
    );
  }
});

The problem is the title and body are currently static. How do I extract the response body and used that to dynamically create custom notification messages instead?