code: function (key, callbackId) {
      const sender = this.sender
      if (!supportLocalStorage) {
        return callNotSupportFail(sender, callbackId)
      }
      if (!key) {
        sender.performCallback(callbackId, {
          result: FAILED,
          data: INVALID_PARAM
        })
        return
      }
      try {
        const val = localStorage.getItem(key)
        sender.performCallback(callbackId, {
          result: val ? SUCCESS : FAILED,
          data: val || UNDEFINED
        })
      }
      catch (e) {
        // accept any exception thrown during a storage attempt as a quota error
        callFail(sender, callbackId)
      }
    }
docs: When passed a key name, will return that key's value.
  @param {string} key
  @param {function} callbackId