A service worker that refreshes out of date cookies automatically

cookie-refresh-service-worker.js

// Pseudo-code implementation of a service worker which refreshes cookies
//   whenever a request is intercepted from the page and the cookie hasn't been
//   refreshed already in the last 30 minutes.

// Note: implementation assumes the following global methods:
// getLastRefreshTime: a function which returns the time we last performed a
//   cookie refresh, or 1970 if setLastRefreshTimeToNow has never been called
// setLastRefreshTimeToNow: a function which sets the future results of
//   getLastRefreshTime to now

// Note in the future we should use getCookies to actually check the expiry
//  date on the current cookies, but that is currently unavailable so we simply
//  do it every 30 minutes always.

self.addEventListener('fetch', (e) => {
  // If we haven't refreshed the cookies in more than 30 minutes...
  // Note: pseudocode time comparison
  if (getLastRefreshTime() > 30 minutes) {
    // Respond by first refreshing cookies, then actually executing the
    //   intercepted request. Note we must set credentials to 'include'
    //   if we want the Set-Cookie header to apply
    e.respondWith(fetch('/refreshCookie', { credentials: 'include' }).then(() => {
      console.log('I haz a new cookie!');
      // TODO: Only include credentials on requests that are supposed to send
      //   cookies
      // Execute the intercepted request and pass it back to the page
      return fetch(e.request, {
        credentials: 'include'
      }).then((response) => {
        setLastRefreshTimeToNow();
        return response;
      });
    }));
  }
});