利用formdata异步上传图片并预览图片

<img src="" style="width: 120px;margin-bottom: 5px" id="previewimg0">
<form action="" enctype="multipart/form-data" id="form0">
   <input type="file"  name="file" id="file0" onChange="preview(this,0)" style="width: 70px;margin-left: 25px">
</form>

function preview(obj,id){
       var img = document.getElementById("previewimg"+id);
       img.src = window.URL.createObjectURL(obj.files[0]);
       var data = new FormData($('#form'+id)[0]);
       $.ajax({
           url: 'uploadoption.php',
           type: 'POST',
           data: data,
           dataType: 'JSON',
           cache: false,
           processData: false,
           contentType: false
       }).done(function(ret){
           if(ret['isSuccess']){
               img.src = window.URL.createObjectURL(obj.files[0]);
           }else{
               alert('提交失敗');
           }
       });

   }

<?php
$file = $_FILES['file'];//得到传输的数据
$Name = $file['name'];//得到文件名称

$type = strtolower(substr($Name,strrpos($Name,'.')+1));//得到文件类型。转为小写
$allow_type = array('jpg','jpeg','gif','png');//定义允许上传的类型
//判断文件类型是否允许上传
if(!in_array($type,$allow_type)){
   //如果不允许，直接停止
   return;
}
//判读是否通过http post上传
if(!is_uploaded_file($file['tmp_name'])){
   return;
}
$upload_path = "image/";//上传文件的存放路径
//开始移动文件到相应的文件夹
if(move_uploaded_file($file['tmp_name'],$upload_path.$file['name'])){
   $response['isSuccess'] = true;
   $response['photo'] = $upload_path.$file['name'];
}else{
   $response['isSuccess'] = false;
}

//$picture = $upload_path.$file['name'];
echo json_encode($response);