Total size, in bytes, of all entries in the Cache Storage API

cache-size.js

// Note that any opaque (i.e. cross-domain, without CORS) responses in the cache will return a size of 0.
caches.keys().then(cacheNames => {
  let total = 0;
  return Promise.all(
    cacheNames.map(cacheName => {
      // Change this to match the cache name filter you want.
      if (!cacheName.includes('sw-precache')) {
        return;
      }
      
      return caches.open(cacheName).then(cache => {
        return cache.keys().then(keys => {
          return Promise.all(
            keys.map(key => {
              return cache.match(key)
                .then(response => response.arrayBuffer())
                .then(buffer => total += buffer.byteLength);
            })
          );
        });
      });
    })
  ).then(() => console.log(`Total bytes: ${total}`));
});