如何在类似树的数组列表中找到最后一个子项

function findLastChild(tree) {
    let lastChild = null;
    let maxDepth = -1;

    function dfs(node, depth) {
        if (depth > maxDepth) {
            maxDepth = depth;
            lastChild = node;
        }
        if (node.children && node.children.length > 0) {
            for (let child of node.children) {
                dfs(child, depth + 1);
            }
        }
    }

    for (let root of tree) {
        dfs(root, 0);
    }

    return lastChild;
}

// 示例树形数组列表
const tree = [
    {
        id: 1,
        children: [
            { id: 2 },
            { id: 3, children: [{ id: 4 }] }
        ]
    },
    {
        id: 5,
        children: [
            { id: 6 },
            { id: 7, children: [{ id: 8, children: [{ id: 9 }] }] }
        ]
    }
];

console.log(findLastChild(tree)); // 输出最后一个子项，例如 { id: 9 }