Delete a cache file when a new one is ON with active

js

self.addEventListener('activate', function(event) {
  event.waitUntil(
      caches.keys().then(function (cacheNames) {
          return Promise.all(
              cacheNames.filter(function (cacheNames) {
                  return cacheNames.startsWith('wittr-') &&
                      cacheNames !== staticCacheName;
              }).map(function (cacheNames) {
                  return caches.delete(cacheNames);
              })
          )
      }
  );
});