使用dropzone.js的异步完成条件

Question

我有一个包含三个dropzones的页面，每个dropzones调用一个函数，一旦它们完成就更新站点上的图像。问题是如果同时上传三个文件，则在三个文件中的最后一个完成上载之前不会触发该功能。有没有办法在每次上传文件时触发函数的迭代？

使用Javascript：

var updatePreview = function(page) {
    $.ajax({
        url: 'submit.php',
        type:'GET',
        success: function(data){
            var pageSize = '',
                source_preview = '',
                source_preview_background = '';

            if ($(data).find('#file_0' + page + ' .ledger_preview').length) {
                //If paper is ledger-size
                source_preview = $(data).find('#file_0' + page + ' .ledger_preview'),
                source_preview_background = source_preview.css('background-image');
                $('#file_0' + page + ' .ledger_preview').css('background-image', source_preview_background);
            }
            else {
                //If paper is letter-size
                source_preview = $(data).find('#file_0' + page + ' .letter_preview'),
                source_preview_background = source_preview.css('background-image');
                $('#file_0' + page + ' .letter_preview').css('background-image', source_preview_background);
            }
       }
    });
};

Dropzone.autoDiscover = false;

var dzOne = new Dropzone('#file-one', {
    url: 'submit.php',
    paramName: 'file_01',
    method: 'POST',
    init: function() {
        this.on('complete', function() {
            updatePreview('1');
        });
    },
    accept: function(file, done) {
        done();
    }
});

var dzTwo = new Dropzone('#file-two', {
    url: 'submit.php',
    paramName: 'file_02',
    method: 'POST',
    init: function() {
        this.on('complete', function() {
            updatePreview('2');
        });
    },
    accept: function(file, done) {
        done();
    }
});

var dzThree = new Dropzone('#file-three', {
    url: 'submit.php',
    paramName: 'file_03',
    method: 'POST',
    init: function() {
        this.on('complete', function() {
            updatePreview('3');
        });
    },
    accept: function(file, done) {
        done();
    }
});