关于JS提交file 上传文件

 最近因写一个上传功能，不能刷新页面，且页面得有后台返回的信息，因而不能使用form直接提交表单，尝试使用is提交并接受返回数据，不多说代码如下：

前台：
<form id=‘pdf-form‘ enctype="multipart/form-data" method="POST"  action="" >
    <input type="hidden" name="order_id" value="<{$order.order_id}>">
    <table align="center" width="90%" border="0">
        <tr>
            <td><b>合同信息：</b>
                <a target="_self" href="<{link app=b2c ctl=site_paycenter act=download arg0=$contract_no}>" class="active">下载</a></td>
            <{if $sign ==1}>
            <td>
                <input type="file" name="inputpdf" id="inputpdf">
                <{button id="button" onclick="upload(this);"  class="btn-import" label="合同上传"}>
                <span id="span" style="display: none" class="success notice-inline">上传成功！</span>
            </td>
            <{/if}>
        </tr>
    </table>
</form>
js:
function upload(o){
    var data = new FormData(document.getElementById(‘pdf-form‘));
    data.append(‘CustomFile‘,‘this is data‘);
    var PDF = new XMLHttpRequest();
    PDF.open("post",‘<{link app=b2c ctl=site_paycenter act=uploadFile}>‘,true);
    PDF.onload = function(){
        if(PDF.status == 200){
            re =JSON.decode(PDF.responseText);
            console.log(re);
            if( re.rsp == ‘succ‘){
                document.getElementById(‘button‘).style.display= ‘none‘;
                document.getElementById("span").innerHTML=re.res;
                document.getElementById(‘span‘).style.display= ‘‘;
               // document.getElementById("url").href=‘.‘+re.url;
            }else{
                document.getElementById("span").innerHTML=re.res;
                document.getElementById(‘span‘).style.display= ‘‘;
            }
        }
    };
    PDF.send(data);
}
后台处理以及返回信息：
function uploadFile()
{
    $file = $_FILES[‘inputpdf‘][‘name‘];
    $filetempname = $_FILES[‘inputpdf‘][‘tmp_name‘];
    $filelist = explode(‘.‘,$file);
    $type = end($filelist);
    if($type != ‘pdf‘){
        $return = array (
            ‘rsp‘ => ‘fail‘,
            ‘res‘ => ‘请上传pdf文件！‘,
        );
        echo json_encode($return);exit;
    }
    //自己设置的上传文件存放路径
    $filePath = ‘./public/pdf/‘;
    $contract_name = $file;
    $string_md5 = md5 (md5($contract_name).time());
    $front_string = substr ($string_md5 ,0 ,31 );
    $contract_url = ‘s‘.$front_string.‘.pdf‘;    //pdf名称

    $uploadfile = $filePath .$contract_url;//上传后的文件名地址
    //move_uploaded_file() 函数将上传的文件移动到新位置。若成功，则返回 true，否则返回 false。
    $result = move_uploaded_file($filetempname, $uploadfile);//假如上传到当前目录下

    if($result == true){
        $orders = app::get(‘b2c‘)->model(‘orders‘)->getList(‘contract_no‘, array(‘order_id‘=>$_POST[‘order_id‘]));  //获取用户发票信息
        $contracts = app::get(‘b2c‘)->model(‘contract_list‘)->getList(‘*‘, array(‘contract_no‘=>$orders[0][‘contract_no‘]));  //获取用户默认收货地址

        $contract_no = $orders[0][‘contract_no‘];
        $delfile = $contracts[0][‘contract_url‘];
        $contracts[0][‘contract_url‘] = $uploadfile;
        $contracts[0][‘contract_name‘] = $contract_name;
        $contracts[0][‘uptime‘] = date(‘Y-m-d H:i:s‘,time());
      //  unset($contracts[0][‘id‘]);
        $flag = app::get(‘b2c‘)->model(‘contract_list‘)->update($contracts[0],array(‘id‘=> $contracts[0][‘id‘]));
        if($flag){
            if(file_exists($delfile)){
                unlink($delfile);
            }
            $return = array (
                ‘rsp‘ => ‘succ‘,
                ‘url‘ => "/paycenter-download-$contract_no.html",
                ‘res‘ => ‘上传成功！‘,
            );
            echo json_encode($return);exit;
        }
    }else{
        $return = array (
            ‘rsp‘ => ‘fail‘,
            ‘res‘ => ‘上传失败！‘,
        );
        echo json_encode($return);exit;
    }

}