寻找树最后一项父节点，及id匹配项

var obj = {name: "a1", type: 1, children: [], expend: true}
var arr2 = [
    {name: "a1", type: 1, children: [], expend: true},
    {
        name: "a1",
        type: 1,
        children: [],
        expend: true
    }
]
var arr = [
    {name: "a1", type: 1, children: [], expend: true, id: "1"},
    {
        name: "a1",
        id: "2",
        type: 1,
        children: [
            {
                id: "2.1",
                name: "a1",
                type: 1,
                children: [{name: "a1", type: 1, children: [], expend: true, id: "2.1.1"}],
                expend: true
            },
            {
                id: "2.2",
                name: "a1",
                type: 1,
                children: [{name: "a1", type: 1, children: [], expend: true}],
                expend: true
            }
        ],
        expend: true
    }
]
var tempParent = arr

function format(obj, id) {
    if (id) {
        checkId(arr, obj, id)
    } else {
        if (arr.length === 0) {
            arr.push(obj)
        } else {
            checkLast(arr, obj)
        }
    }
}

function checkLast(arr, obj) {
    var length = arr.length
    if (arr[length - 1].expend && arr[length - 1].children.length > 0) {
        tempParent = arr[length - 1].children
        checkLast(arr[length - 1].children, obj)
    } else {
        tempParent.push(obj)
    }
}

function checkId(arr, obj, id) {
    for (var i = 0; i < arr.length; i++) {
        if (arr[i].id === id) {
            arr[i].children.push(obj)
            return
        } else {
            checkId(arr[i].children, obj, id)
        }
    }
}

format(obj, "2.1")

console.log(arr)