function findPathById(id, Tree) {
    let res = []
    function get(tree, arr = []) {
      Array.isArray(tree) && tree.forEach(val => {
        let arrX = JSON.parse(JSON.stringify(arr)) //拷贝一下数组
        arrX.push(val.name)
        val.id === id ? (res = arrX) : val.children && get(val.children, arrX)
      })
    }
    get([Tree])
    return res.join(",")
  }
  const str = findPathById(4, Tree)

const tree = {
    id: 1,
    name: "中国",
    children: [
        {
            id: 2, name: "北京市", children: [
                { id: 3, name: "朝阳区", children: [] },
                { id: 4, name: "海淀区", children: [] },
            ]
        },
        {
            id: 5, name: "上海市", children: [
                { id: 6, name: "徐汇区", children: [] },
                { id: 7, name: "黄浦区", children: [] },
            ]
        },
    ]
}

function findPathById(id) {
    const path = [];
    
    const find = (node, depth, id) => {
        path[depth] = node;
        if(node.id === id) {
            return node;
        }

        for(let n of node.children) {
            const result = find(n, depth + 1, id);
            if(result) {
                path[depth + 1] = n;
                return result;
            }
        }
    }
    find(tree, 0, id);
    return path.reduce((acc, e) => acc + e.name, '');
}

console.log(findPathById(4));