使用Dropzone上传后获取文件名

Question

我正在尝试使用Dropzone js和PHP上传图像，它可以工作，但我想将文件上传名称保存在PHP变量中，但它失败了。

form.php的

<form method="post" action="new_is_add.php" id="form_first" enctype="multipart/form-data">
    <div class="form-group">
        <div id="my-dropzone" class="dropzone">
            <div class="dz-message" data-dz-message>
                <span>
                    Max 2 files
                </span>
            </div>
        </div>
    </div>
    <div class="text-center">
        <button type="submit" name="submit_new" id="submit_new" class="btn btn-primary">Valider</button>
    </div>
</form>
<script type="text/javascript" src="jquery.js"></script>
<script type="text/javascript" src="dropzone.js"></script>    
<script type="text/javascript" src="script.js"></script>

的script.js

var theDate = new Date().getTime();
Dropzone.autoDiscover = false;
var myDropzone = new Dropzone("div#my-dropzone", {
    paramName: "file",
    acceptedFiles: 'image/*',
    maxFiles: 2,
    maxFilesize: 2, // MB
    renameFilename: function (filename) {
        return theDate + '_' + filename;
    },
    url: "new_is_add.php",                      
    autoProcessQueue: false,
});

$('#submit_new').click(function(){           
  myDropzone.processQueue();
});

new_is_add.php

if(!empty($_FILES)){
    $targetDir = "uploads/";
    $fileName = $_FILES['file']['name'];
    $targetFile = $targetDir.$fileName;
    move_uploaded_file($_FILES['file']['tmp_name'],$targetFile);
    echo $_FILES['file']['name'];
}

我的$_FILES['file']['name']为空，我该如何获取文件名？