Property 'index' does not exist on type 'Element'

項目啟動報錯，但重新保存js文件又可以運行

toggleDetails() {
      var item = document.getElementsByClassName('list-wrapper');
        var next = document.getElementsByClassName('ico-next');
      var divcard = document.getElementsByClassName('divcard');
      for (var i = 0; i < item.length; i++) {
          item[i].index = i;
          item[i].onclick = function () {
              var num = this.index;
              if (divcard[num].style.display === 'block') {
                  next[num].style.transform = 'rotate(0)';
                  divcard[num].style.display = 'none';
              } else {
                  next[num].style.transform = 'rotate(90deg)';
                  divcard[num].style.display = 'block';
              }
          }
      }
  }