async open (cacheName) {
    webidl.brandCheck(this, CacheStorage)
    webidl.argumentLengthCheck(arguments, 1, { header: 'CacheStorage.open' })

    cacheName = webidl.converters.DOMString(cacheName)

    // 2.1
    if (this.#caches.has(cacheName)) {
      // await caches.open('v1') !== await caches.open('v1')

      // 2.1.1
      const cache = this.#caches.get(cacheName)

      // 2.1.1.1
      return new Cache(kConstruct, cache)
    }

    // 2.2
    const cache = []

    // 2.3
    this.#caches.set(cacheName, cache)

    // 2.4
    return new Cache(kConstruct, cache)
  }
@see https://w3c.github.io/ServiceWorker/#cache-storage-keys
@returns {string[]}