JQuery 动态XML字符串添加节点

<textarea rows="30" cols="65" name="xml" id="xml" style="display:none;">
<?xml version="1.0" encoding="UTF-8" ?>
<AdvPay>
<PubInfo>
    <DigestAlg>MD5</DigestAlg>
    <VerifyCode>xxxxxx</VerifyCode>
</PubInfo>
<BusiData>
    <AccountType>1</AccountType>
    <AccountCode>15868477618</AccountCode>
    <RoyaltyFlag>0</RoyaltyFlag>
</BusiData> 
</AdvPay>
</textarea>

var phone=$('#phone').val();
        var authCode=$('#authCode').val();             
        var text = $('#xml').val();
        //添加AuthCode节点和Phone节点
        var posHead = text.indexOf('<BusiData>');
        var posEnd = text.indexOf('<AccountType>');
        var strHead = text.substring(0, posHead) + '<BusiData>';
        var strEnd = text.substring(posEnd);
        code = '<AuthCode>'+authCode+'</AuthCode><Phone>'+phone+'</Phone>';
        $('#xml').val(strHead + code + strEnd);