在百度前端学院中斌斌学院任务八，用二叉树依次显示，经过几轮后就找不到nodevalue属性

function preOrder(node) {
    if (!(node == null)) {
        lists.push(node);
        var allChild = node.children;
        for (let i = 0; i < allChild.length; i++) {
          preOrder(allChild[i]);
        }
    }
}

function changeColor() {
    var i = 0;
    // lists[i].style.backgroundColor = "red";
    timer = setInterval(function(){
      if (i<lists.length) {
        if (i>0) {
            lists[i-1].style.backgroundColor = "#fff";
        }
        lists[i].style.backgroundColor = "grey";
        if (lists[i].firstChild.nodeValue == content.value) {
          lists[i].style.border = "1px bold red";
          bool = true;
        }
      }else{
        clearInterval(timer);
        lists[i-1].style.backgroundColor = "#fff";
      }
      i++;
    },500)
}

function clear() {
    clearInterval(timer);
    lists = [];
}