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 (i0) { 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 = []; }