thinkphp5 返回json后沒有l(wèi)ength屬性？

function findChild(&$arr,$id){
        $childs=array();
        foreach ($arr as $k => $v){
            if($v['pid']== $id){
                $childs[]=$v;
            }
        }
        return $childs;
    }

    function build_tree($rows,$root_id){
        $childs=$this->findChild($rows,$root_id);
        if(empty($childs)){
            return '[]';
        }
        foreach ($childs as $k => $v){
            $rescurTree=$this->build_tree($rows,$v['id']);
            if( null != $rescurTree){
                $childs[$k]['data']=$rescurTree;
            }
            $childs[$k]['value'] = $v['id'];
        }
        return $childs;
    }

    public function test(){
        $sql = db('auth_rule')->select();
        $data = $this->build_tree($sql,0);
        return json($data) ;
    }

返回的json：

[{
    "id": 1,
    "name": "sys",
    "title": "系統(tǒng)設(shè)置",
    "type": 1,
    "status": 1,
    "condition": "",
    "pid": 0,
    "level": 0,
    "sort": 7,
    "data": [{
        "id": 11,
        "name": "conf\/lst",
        "title": "配置列表",
        "type": 1,
        "status": 1,
        "condition": "",
        "pid": 1,
        "level": 1,
        "sort": 50,
        "data": [{
            "id": 12,
            "name": "conf\/add",
            "title": "添加配置",
            "type": 1,
            "status": 1,
            "condition": "",
            "pid": 11,
            "level": 2,
            "sort": 50
        }, {
            "id": 13,
            "name": "conf\/del",
            "title": "配置刪除",
            "type": 1,
            "status": 1,
            "condition": "",
            "pid": 11,
            "level": 2,
            "sort": 50
        }, {
            "id": 14,
            "name": "conf\/edit",
            "title": "配置編輯",
            "type": 1,
            "status": 1,
            "condition": "",
            "pid": 11,
            "level": 2,
            "sort": 50
        }]
    }, {
        "id": 9,
        "name": "conf\/conf",
        "title": "配置項(xiàng)",
        "type": 1,
        "status": 1,
        "condition": "",
        "pid": 1,
        "level": 1,
        "sort": 50
    }]
}, {
    "id": 15,
    "name": "admin",
    "title": "管理員",
    "type": 1,
    "status": 1,
    "condition": "",
    "pid": 0,
    "level": 0,
    "sort": 50,
    "data": [{
        "id": 16,
        "name": "admin\/lst",
        "title": "管理員列表",
        "type": 1,
        "status": 1,
        "condition": "",
        "pid": 15,
        "level": 1,
        "sort": 50,
        "data": [{
            "id": 17,
            "name": "admin\/add",
            "title": "管理員添加",
            "type": 1,
            "status": 1,
            "condition": "",
            "pid": 16,
            "level": 2,
            "sort": 50
        }, {
            "id": 18,
            "name": "admin\/del",
            "title": "管理員刪除",
            "type": 1,
            "status": 1,
            "condition": "",
            "pid": 16,
            "level": 2,
            "sort": 50
        }, {
            "id": 19,
            "name": "admin\/edit",
            "title": "管理員修改",
            "type": 1,
            "status": 1,
            "condition": "",
            "pid": 16,
            "level": 2,
            "sort": 50
        }]
    }]
}]

但是用js去獲取res.length的時候，卻提示cannot read property 'length' of undefined

回答

編輯回答

落殤

cannot read property 'length' of undefined

的意思是undefined沒有length屬性，說明說你的res是undefined，undefined當(dāng)然沒有length屬性了。

為啥res會是undefined？不是在控制臺里打印出來了嗎？有兩種可能，第一種是你打印的根本就不是同一個res.length（作用域的問題)，第二種，也是我認(rèn)為非常有可能的，就是你還沒搞懂js的異步，前端在發(fā)請求的時候需要你提供一個“回調(diào)函數(shù)”，只有在這個回調(diào)函數(shù)里你才能獲得res。比如

let res;
$.get(url, data => res = data);
console.log(res);  // undefined
res.length  // cannot read property 'length' of undefined

$.get(url, data => {
  console.log(data);
  console.log(data.length);
  // do something here
});

2017年2月25日 14:16

編輯回答