SOURCE

let arr = [
    { id: 1, name: '部门1', pid: 0 },
    { id: 2, name: '部门2', pid: 1 },
    { id: 3, name: '部门3', pid: 1 },
    { id: 4, name: '部门4', pid: 3 },
    { id: 5, name: '部门5', pid: 4 },
]
// 递归方法
function getChild(data, pid) {
    var arr = [];
    data.forEach(e => {
        if (e.pid === pid) {
            e.children = arguments.callee(data, e.id)
            arr.push(e)
        }
    })
    return arr;
}
function toTree(arr, pid) {
    var tree = []
    tree = getChild(arr, pid)
    return tree
}
console.log(ToTree2(arr, 0))

//map方式
function ToTree2(items, pidF) {
    const result = [];   // 存放结果集
    const itemMap = {};  // 
    items.forEach(e => {
        const { id, pid } = e;
        if (!itemMap[id]) {
            itemMap[id] = {
                children: [],
            }
        }
        itemMap[id] = {
            ...e,
            children: itemMap[id]['children']
        }
        if (pid === pidF) {
            result.push(itemMap[id]);
        } else {
            if (!itemMap[pid]) {
                itemMap[pid] = {
                    children: [],
                }
            }
            itemMap[pid].children.push(itemMap[id])
        }
    })
    return result;
}