SW to redirect users to dedicated offline page when disconnected

sw.js

const OFFLINE_URL = '/offline';
self.addEventListener('install', function(e) {
  e.waitUntil(
    caches.open('jungledragon').then(function(cache) {
      return cache.addAll([
        OFFLINE_URL, '/'
      ]);
    })
  );
});

self.addEventListener('fetch', event => {
  // only listen to requests for HTML pages, ignore all other network requests
  if (event.request.mode === 'navigate' || (event.request.method === 'GET' && event.request.headers.get('accept').includes('text/html'))) {
    // if the HTML fetch fails, forcefully redirect users to the cached offline page
    event.respondWith(
      fetch(event.request).catch(error => {
        return caches.match(OFFLINE_URL);
      })
    );
  }
});