PWA Day06 - remove outdate cache

sw.js

self.addEventListener('activate', function(event) {
  event.waitUntil(
    caches
      .keys()
      .then(function(cacheNames) {
        return Promise.all(
          cacheNames
            .filter(function(cacheName) {
              // Return true if you want to remove this cache,
              // but remember that caches are shared across
              // the whole origin
            })
            .map(function(cacheName) {
              return caches.delete(cacheName)
            })
        )
      })
  )
})