headers.js

let headers = new Headers();
headers.append('X-Food', 'Candy Corn');
headers.append('X-Drink', 'Cider');

let request = new Request('/order.html');

autoHeaders.put(request, headers);

preload.js

let headers = new Headers();
headers.append('X-Preload-Value', 'Boo');

let request = new Request('/order.html', {
  // spec service worker preload requests to include 'ServiceWorkerPreload' header
  headers: { Vary: 'ServiceWorkerPreload' }
});

autoHeaders.put(request, headers);