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 },
];
let result = [];
function arrayToTree1(items) {
    const result = [];
    const itemMap = {};

    for (const item of items) {
        itemMap[item.id] = { ...item, children: [] };
    }

    for (const item of items) {
        const id = item.id;
        const pid = item.pid;
        const treeItem = itemMap[id];
        if (pid === 0) {
            result.push(treeItem);
        } else {
            if (!itemMap[pid]) {
                itemMap[pid] = {
                    children: [],
                };
            }
            itemMap[pid].children.push(treeItem);
        }
    }

    return result;
}
result = arrayToTree1(arr);
// console.log(result);
console.log(JSON.stringify(result));
console.log("========");

function arrayToTree2(items) {
    const result = [];
    const itemMap = new Map();
    let pid0id;
    items.map((item, index) => {
        itemMap.set(item.id, { ...item, children: [] });
    });

    items.map((item, index) => {
        const id = item.id;
        const pid = item.pid;
        const treeItem = itemMap.get(id);

        if (pid === 0) {
            result.push(treeItem);
        } else {
            if (!itemMap.get(pid)) {
                itemMap.set(pid, { children: [] });
            }
            const _item = itemMap.get(pid);
            _item.children.push(treeItem);
        }
    });

    return result;
}
// result = arrayToTree2(arr);
// console.log(result);
// console.log(JSON.stringify(result));

function arrayToTree3(arr) {

    const itemMap = {};
    for (const item of arr) {
        item.children = [];
        itemMap[item.id] = item;
    }
    // 将对象添加至父节点
    for (const item of arr) {
        const parent = itemMap[item.pid];
        if (parent) {
            parent.children.push(item);
        }
    }

    const result = arr.filter((item) => item.pid == 0);
    console.log(JSON.stringify(result));
    return result;
}
result = arrayToTree3(arr);