How to use the @angular/service-worker/worker.cacheFromNetworkOp function in @angular/service-worker

      .map(url => cacheFromNetworkOp(this.worker, url.url, this.cacheKey)));
  }

.then(resp => {
          if (!!resp) {
            LOG.technical(`setup(${this.cacheKey}, ${url}): no need to refresh ${url} in the cache`);
            return null;
          }
          LOG.technical(`setup(${this.cacheKey}, ${url}): caching from network`);
          return cacheFromNetworkOp(this.worker, url, this.cacheKey, shouldCacheBust(url))();
        })
      }