一 数组转树形结构的方法

{
	"city": [{
			"id": 12,
			"parent_id": 1,
			"name": "朝阳区"
		},
		{
			"id": 241,
			"parent_id": 24,
			"name": "⽥林街道"
		},
		{
			"id": 31,
			"parent_id": 3,
			"name": "⼴州市"
		},
		{
			"id": 13,
			"parent_id": 1,
			"name": "昌平区"
		},
		{
			"id": 2421,
			"parent_id": 242,
			"name": "上海科技绿洲"
		},
		{
			"id": 21,
			"parent_id": 2,
			"name": "静安区"
		},
		{
			"id": 242,
			"parent_id": 24,
			"name": "漕河泾街道"
		},
		{
			"id": 22,
			"parent_id": 2,
			"name": "⻩浦区"
		},
		{
			"id": 11,
			"parent_id": 1,
			"name": "顺义区"
		},
		{
			"id": 2,
			"parent_id": 0,
			"name": "上海市"
		},
		{
			"id": 24,
			"parent_id": 2,
			"name": "徐汇区"
		},
		{
			"id": 1,
			"parent_id": 0,
			"name": "北京市"
		},
		{
			"id": 2422,
			"parent_id": 242,
			"name": "漕河泾开发区"
		},
		{
			"id": 32,
			"parent_id": 3,
			"name": "深圳市"
		},
		{
			"id": 33,
			"parent_id": 3,
			"name": "东莞市"
		},
		{
			"id": 3,
			"parent_id": 0,
			"name": "⼴东省"
		}
	]
}

• 递归方法

function arrayToTree(list, root) {
	return list.filter(item => item.parent_id === root).map(item => ({
		...item,
		children: arrayToTree(list, item.id)
	}))
}