数组转树

// 原始数据如下：
let source = [
    {id: 0, name: '部门一', parentId: null},
    {id: 1, name: '部门二', parentId: 0},
    {id: 2, name: '部门三', parentId: 1},
    {id: 3, name: '部门四', parentId: 2},
    {id: 4, name: '部门五', parentId: 2}
]
// 输出

    let result = {
        id: 0,
        name: '部门一',
        children: [
            {
                id: 1, 
                name: '部门二',
                childern: [
                    {
                        id: 2,
                        name: '部门三',
                        childern: [
                            {
                                id: 3,
                                name: '部门四',
                                childern: []
                            },
                            {
                                id: 4,
                                name: '部门五',
                                childern: []
                            }
                        ]
                    }
                ]
            }
        ]
    }

方法一：forEach找儿子法

function findChid(arr) {
    arr.forEach(item => {
        item.childern = arr.filter(subItem => subItem.parentId === item.id)
    })
    return arr.find(item => item.parentId === null)
}

方法二： forEach找爹法

function findParent(arr) {
    let result;
    arr.forEach(item => {
        let p = arr.find(subItem => subItem.id === item.parentId);
        if (p) {
            if (p.children) {
                p.children.push(item);
            } else {
                p.children = [];
                p.children.push(item);
            }
        } else {
            result = item;
        }
    })
    return result;
}