[rbdr/r.bdr.sh] / service_worker.js

'use strict';

const internals = {
  version: '4.2.0',
  offlineEssentials: [
    '/',
    '/css/application.css'
  ],

  // Response for when network is not available

  errorResponse: '<h1>Service Unavailable</h1>',

  // Main entry point, adds event listeners for service worker

  main() {

    self.addEventListener('install', internals.onInstall);
    self.addEventListener('fetch', internals.onFetch);
    self.addEventListener('activate', internals.onActivate);
  },

  // Runs on installation of the service worker

  onInstall(event) {

    event.waitUntil(
      caches.open(`${internals.version}/essentials`)
        .then((cache) => {

          return cache.addAll(internals.offlineEssentials)
        })
    );
  },

  // Runs when a path is fetched, returns files from cache

  onFetch(event) {

    if (event.request.method !== 'GET') {
      return;
    }

    event.respondWith(
      caches.match(event.request)
        .then((cached) => {

          const freshContent = fetch(event.request)
            .then((response) => {

              caches.open(`${internals.version}/paths`)
                .then((cache) => cache.put(event.request, response.clone()));
            }, internals.onFetchFail)
            .catch(internals.onFetchFail);

            return cached || freshContent;
        })
    );
  },

  onActivate(event) {

    event.waitUntil(
      caches.keys()
        .then((keys) => {

          return Promise.all(keys
            .filter((key) => !key.startsWith(internals.version))
            .map((key) => caches.delete(key))
          );
        })
    );
  },

  // Responds with Servie Unavailable if we can't fetch a
  // file from network

  onFetchFail() {

    return new Response(internals.errorResponse, {
      status: 503,
      statusText: 'Service Unavailable',
      headers: new Headers({
        'Content-Type': 'text/html'
      })
    });
  }
};

internals.main();