在正确发布ajax之前，如何检查图像是否已添加到dropzone中？

Question

我试图编写一个脚本来检查dropzone上是否有任何图像丢失。 我正在使用Twitter bootstrap。

在提交时运行的ajax脚本是：

$.ajax({
    type: method,
    action: action,
    data: formdata,
    processData: false,
    contentType: false,
    dataType: 'json',
    beforeSend: function(xhr) {
        if (myDropzone.getQueuedFiles().length == 0) {
            // I've managed to get the values of the number of images dropped.
            // I want to inform the user that they've not added any images,
            // They can continue to submit without adding images if they click on continue on the modal
            // Or click cancel and drop some images.
        }
    },
    success: function(data) {
        console.log(data);
    },
    error: function(data) {
        var errors = data.responseJSON;
            console.log(data);
            $.each(errors, function(key, value) {
                $('#' + key).after('<div class="alert alert-danger">' + value + '</div>');
            });
    }

});

我不确定如何实现这一目标。感谢您阅读