PHP+JavaScriptで画像を更新せずにアップロード可能

<!-- ajax文件上传开始 -->
<script type="text/javascript" src="/imageupload/jquery-1.10.2.min.js"></script>
<script type="text/javascript" src="/imageupload/layer/layer.js"></script>
<script type="text/javascript" src="/imageupload/ajaxupload.js"></script>
<!--ajax文件上传结束-->
<!--上传文件按钮列表开始-->
<input id="requesturl" type="hidden" value="{:U(&#39;admin/upload/uploadfile&#39;)}" />
<input id="ajaxuploadfile" type="file" onchange="filechange()"/>
<input id="filepathurl" type="hidden" value="" />
<input type="button" value="第一张" pathurl="./Uploads/admin/trailer/" class="uploadclass" />
<input type="button" value="第二张" pathurl="./Uploads/admin/fdfdfd/" class="uploadclass" />
<input type="button" value="第三张" pathurl="./Uploads/admin/cdcdfd/" class="uploadclass" />
<!--上传文件按钮列表结束-->

/**
* 文件上传方法
*/
public function uploadfile(){
//单文件上传
$upload = new \Think\Upload();// 实例化上传类
$upload->maxSize = 100000000 ;// 设置附件上传大小
$upload->exts = array('jpg', 'gif', 'png', 'jpeg');// 设置附件上传类型
$url = $_POST['filepathurl'];
if (!file_exists($url)){
mkdir ($url,0777,true);
}
$upload->rootPath = $url; // 设置附件上传根目录
// 上传单个文件
$info = $upload->uploadOne($_FILES['postfilename']);
if(!$info) {
echo json_encode(array('bool'=>false,'error'=>$upload->getError()));
}else{
$path = $info['savepath'].$info['savename'];
echo json_encode(array('bool'=>true,'path'=>$path));
}
}