web前端 ajax请求上传图片数据类型处理

form: function (url, paras, files, success) {
//上传的文件类型是MultipartFile[]
//如果把需要的参数直接传入，则会请求错误
//设置请求参数的数据类型
            var urlStr = UrlParas(url, paras).url;
            console.log(urlStr)
var formData = new FormData();
for (var item in paras) {
                formData.append(item, paras[item]);
            }

            for (var item in files) {
                for (var i = ; i < files[item].length; i++) {
                    formData.append(item, files[item][i]);
                }
            }
            console.log(formData)
            return;
            $.ajax({
                url: urlStr,
                data: formData,
                type: 'post',
                contentType: false,
                processData: false,
                success: success,
                error: function (msg) {
                    errorState(msg);
                }
            });
        }