json文件_ajax

html源码代码：

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>ajax json jquery 菜单案例</title>
<style type="text/css">
*{margin:;padding:;}
body { font-size: 13px; line-height: %; padding: 60px }
</style>
<link rel="stylesheet" type="text/css" href="../css/style.css"/>
<script src="../js/jquery-2.1.1.min.js"></script>
<script type="text/javascript">
$(function(){
$("#first").change(function() {
var id=document.getElementById("first").value;
 $.ajax({
     type: "POST",
     url: "../data/menu.json",
     dataType: "json",
    success: function(data) {
        var secondRoot=document.getElementById("second");
        secondRoot.innerHTML=null;
        for(var i=;i<data.length;i++)
        {
            if(data[i].cid==id)
            {
                for( var j=;j<data[i].cname.length;j++)
                {
                    var op = document.createElement("option");
                    op.innerHTML=(data[i].cname)[j];
                    secondRoot.appendChild(op);
                }
            }
        }
    },
    error:function(data){
        alert(data);
    }
    });
});
});

</script>
</head>
<body>
   <select name="first" id="first" style="width:160px">
        <option value="">---请选择---</option>
        <option value="" >中国</option>
        <option value="">美国</option>
        <option value="">英国</option>
    </select>
    <select name="second" id="second" size="" style="width:160px"></select>
</body>
</html>

json源代码

[
    {
        "cid": "",
        "cname": [
            "子菜单1",
            "子菜单1",
            "子菜单1"
        ]
    },
    {
        "cid": "",
        "cname": [
            "子菜单2",
            "子菜单2",
            "子菜单2"
        ]
    },
    {
        "cid": "",
        "cname": [
            "子菜单3",
            "子菜单3",
            "子菜单3"
        ]
    }

]