数组转树

将input数据格式转换为output数据格式

let input =  [{
    id: 1, val: '学校',  parentId: null
},{
    id: 2, val: '班级1', parentId: 1
},{
    id: 3, val: '班级2', parentId: 1
},{
    id: 4, val: '学生1', parentId: 2
},{
    id: 5, val: '学生2', parentId: 3
},{
    id: 6, val: '学生3', parentId: 3
}]

let output = {
    id: 1,
    val: '学校',
    children: [{
        id: 2,
        val: '班级1',
        children: [
            {
                id: 4,
                val: '学生1',
                children: []
            }
        ]
    }, {
        id: 3,
        val: '班级2',
        children: [
            {
                id: 5,
                val: '学生2',
                children: []
            },{
                id: 6,
                val: '学生3',
                children: []
            }
        ]
    }]
}

实现方式

function arrToTree(input){
    let { id,val } = input.find(item => item.parentId === null)
    let output = {
        id,val
    }
    let toTree = (id,input) => {
        let children = []
        for(let i = 0;i < input.length;i++){
            let item = input[i]
            if(id == item.parentId){
                children.push({
                    id:item.id,
                    val:item.val,
                    children:toTree(item.id,input)
                })
            }
        } 
        return children
    }
    output.children = toTree(id,input)
    return output
}