JavaScriptのService Worker入門｜オフライン対応とキャッシュ制御

if ('serviceWorker' in navigator) {
  navigator.serviceWorker.register('/service-worker.js')
    .then(function(registration) {
      console.log('Service Worker registered with scope:', registration.scope);
    })
    .catch(function(error) {
      console.log('Service Worker registration failed:', error);
    });
}

self.addEventListener('install', function(event) {
  event.waitUntil(
    caches.open('my-site-cache')
      .then(function(cache) {
        return cache.addAll([
          '/',
          '/index.html',
          '/style.css',
          '/script.js'
        ]);
      })
  );
});

self.addEventListener('activate', function(event) {
  var cacheWhitelist = ['my-site-cache'];

  event.waitUntil(
    caches.keys().then(function(cacheNames) {
      return Promise.all(
        cacheNames.map(function(cacheName) {
          if (cacheWhitelist.indexOf(cacheName) === -1) {
            return caches.delete(cacheName);
          }
        })
      );
    })
  );
});

self.addEventListener('fetch', function(event) {
  event.respondWith(
    caches.match(event.request)
      .then(function(response) {
        // Cache hit - return response
        if (response) {
          return response;
        }

        // IMPORTANT: Clone the request. A request is a stream
        // and because we've already consumed it once by matching
        // it to the cache, we need to clone it so that the
        // fetch API can consume it as well.
        var fetchRequest = event.request.clone();

        return fetch(fetchRequest).then(
          function(response) {
            // Check if we received a valid response
            if(!response || response.status !== 200 || response.type !== 'basic') {
              return response;
            }

            // IMPORTANT: Clone the response. A response is a stream
            // and because we need the browser to consume the response
            // as well as the cache consuming the response, we need
            // to clone it so we have two streams.
            var responseToCache = response.clone();

            caches.open('my-site-cache')
              .then(function(cache) {
                cache.put(event.request, responseToCache);
              });

            return response;
          }
        );
      })
    );
});