Cookie parsing
Given the cookie name, get the value of a cookie. You can also use cookies for A/B testing.
import { parse } from 'cookie';
// The name of the cookie
const COOKIE_NAME = '__uid';
function handleRequest(request) {  const cookie = parse(request.headers.get('Cookie') || '');
  if (cookie[COOKIE_NAME] != null) {    // Respond with the cookie value    return new Response(cookie[COOKIE_NAME]);  }
  return new Response('No cookie with name: ' + COOKIE_NAME);
}
addEventListener('fetch', event => {  event.respondWith(handleRequest(event.request));
});