sw_claim_client.js

self.onactivate = function(event) {
  event.waitUntil(
    self.clients.claim().then(function() {
      var currentCacheName = CACHE_NAME + '-v' + CACHE_VERSION;
      return caches.keys().then(function(cacheNames) {
        return Promise.all(
          cacheNames.map(function(cacheName) {
            if (cacheName.indexOf(CACHE_NAME) == -1) {
              return;
            }

            if (cacheName != currentCacheName) {
              return caches.delete(cacheName);
            }
          })
        );
      });
    })
  );
};