elementUI el-tree 修改无子项的样式

　this.$nextTick(() => {

        var levelName = document.getElementsByClassName('is-leaf');

        for (var i = 0; i < levelName.length; i++) {

          // 找到可以加class的div,再判断这个div的div[role='group']有没有项

          const greatGranNode = levelName[i].parentNode.parentNode.parentNode,

            hasChildren = Array.from(greatGranNode.querySelectorAll("div[role='group']")).findIndex(item => item.childNodes.length > 0) > -1;

          if (Array.from(greatGranNode.classList).indexOf('el-tree-node__children') > -1 && !hasChildren) {

            greatGranNode.classList.add('is-flex')

          }

        }

      });