SOURCE

// map保存id和对象的映射关系；map={1:{id:1,name:'qq',parentId: 0},2:{id:2,name:'22',parentId:2}}
function convert(list) {
	const res = []
	const map = list.reduce((res, v) => (res[v.id] = v, res), {})
	for (const item of list) {
		if (item.parentId === 0) {
			res.push(item)
			continue
		}
		if (item.parentId in map) {
			const parent = map[item.parentId]
			parent.children = parent.children || []
			parent.children.push(item)
		}
	}
	return res
}
let list =[
{id:1,name:'部门A',parentId:0},
{id:2,name:'部门B',parentId:0},
{id:3,name:'部门C',parentId:1},
{id:4,name:'部门D',parentId:1},
{id:5,name:'部门E',parentId:2},
{id:6,name:'部门F',parentId:3},
{id:7,name:'部门G',parentId:2},
{id:8,name:'部门H',parentId:4}
];