getElementById("index");
      $index.innerHTML = "";
      for (let i = 0; i < dnsConf.length; i++) {
        appendConfigToIndex(i);
      }
      // 负数表示倒数第几个
      if (configIndex < 0) {
        configIndex += dnsConf.length;
      } else {
        configIndex = Math.min(configIndex, dnsConf.length - 1);
      }
      $index.value = configIndex;
      showConf(configIndex);
    }

    // 拼接新的配置项到下拉菜单
    function appendConfigToIndex(idx) {
      const $index = d