Javascript -按顺序遍历二叉树。最后一个值打印未定义

// 定义二叉树节点
class Node {
  constructor(value) {
    this.value = value;
    this.left = null;
    this.right = null;
  }
}

// 按顺序遍历二叉树并打印最后一个值
function traverseBinaryTree(root) {
  let stack = [];
  let current = root;
  let lastVisited = null;

  while (current || stack.length > 0) {
    if (current) {
      stack.push(current);
      current = current.left;
    } else {
      let node = stack.pop();
      // 记录最后一个访问的节点
      lastVisited = node.value;
      current = node.right;
    }
  }

  if (lastVisited === null) {
    console.log("二叉树为空");
  } else {
    console.log("最后一个值: " + lastVisited);
  }
}

// 创建二叉树
let root = new Node(1);
root.left = new Node(2);
root.right = new Node(3);
root.left.left = new Node(4);
root.left.right = new Node(5);
root.right.left = new Node(6);
root.right.right = new Node(7);

// 按顺序遍历二叉树并打印最后一个值
traverseBinaryTree(root);