Ajax使用一+javascript解析Ajax返回的json字串

//關鍵：點選登入按鈕後，Ajax方法判斷，下面為login.php包含的login.js程式碼
function chklg() {
    if ($('lgname').value == '') {
        alert('輸入姓名');
        $('lgname').focus();
        return false;
    }
    if ($('lgchk').value != $('chknm').value) {
        alert("驗證碼錯誤");
        $('lgchk').focus();
        return false;
    }
    
    //關鍵：Ajax獲取user_login_chk.php資料
    url = 'user_login_chk.php?act=' + (Math.random()) + '&name=' + $('lgname').value + '&pwd=' + $('lgpwd').value;
    xmlhttp.open('get', url, true);

    xmlhttp.send();
    xmlhttp.onreadystatechange = function () {
        if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
            msg = xmlhttp.responseText;
            
            //關鍵：用eval將返回的json字串msg轉為json，並測試json,jsonobj.name
            var jsonobj=eval('('+msg+')');

             //或者下面兩句同樣效果

           var jsonobj='';

           eval('jsonobj='+msg+';');    

            alert(jsonobj.name);
            $('name').innerHTML = jsonobj;

            if (msg == '1') {
                alert("登入成功");
                location = "test.php"
            }
            else {
                alert("登入失敗");

            }
        }


    }
}

下面為user_login_chk.php程式碼

<?php
//只是測試用
session_start();
header('Content-Type:text/html;charset=gb2312');
include_once 'conn/conn.php';
$name = $_GET['name'];
$pwd = $_GET['pwd'];
if(!empty($name) && !empty($pwd)){
    $sql = "select name from tb_member where name = '".$name."'";

    $num = $conne->getRowsNum($sql);
    //$student為測試用的php陣列，
    $student = array("name"=>"lisheng","age"=>"35");
    $studentJson = json_encode($student);

    if($num == 0 || $num == '' ){
        $reback = $studentJson;
    }else{
        $reback = $studentJson;
    }
}
echo $reback;

?>