/*
        *   ajax上传文件
        *       url                 文件上传地址
        *       fileSelector        input=file 选择器（支持多文件上传，只要后台接口支持）
        *       size                文件限制大小
        *       fileType            文件限制类型 mime类型
        *       success             上传成功处理
        *       error               上传失败处理
        *       timeout             超时处理
        *
        *   return: status:  0      请选择文件
        *                    1      超出文件限制大小
        *                    2      非允许文件格式
        * */
        upload:function(url,fileSelector,size,fileType,success,error,timeout){
            var formdata = http://www.mamicode.com/new FormData(),fileNode = document.querySelector(fileSelector),fileCount = fileNode.files.length,data={},result ={};"status"] = 1;
                        result["errMsg"] = "超出文件限制大小";
                    }else{
                        //检查文件格式.因为支持formdata，自然支持数组的indexof(h5)
                        if (fileType.indexOf(value.type)=== -1 ){
                            result["status"] = 2;
                            result["errMsg"] = "非允许文件格式";
                        }else{
                            formdata.append(value.name,value);
                        };
                    };
                });
            }else{
                result["status"] = 0;
                result["errMsg"] = "请选择文件";
            };

            if (result.status !== undefined)  return result;   //如果有错误信息直接抛出去,结束运行

            var ajaxParam ={
                type:"post",
                url:url,
                data:formdata,
                isFormData:true,
                success:success,
                error:error,
                timeout:timeout
            };
            ajax.common(ajaxParam);
        },
    };

　　　　[Route("upload3")]
        public async Task<HttpResponseMessage> PostFormData()
        {
            // Check if the request contains multipart/form-data.
            // 检查该请求是否含有multipart/form-data
            if (!Request.Content.IsMimeMultipartContent())
            {
                throw new HttpResponseException(HttpStatusCode.UnsupportedMediaType);
            }

            string root = HttpContext.Current.Server.MapPath("~/uploadfile");
            var provider = new ReNameMultipartFormDataStreamProvider(root);

            try
            {
                // Read the form data.
                // 读取表单数据
                var task = await Request.Content.ReadAsMultipartAsync(provider).ContinueWith(t =>
                {
                    if (t.IsFaulted || t.IsCanceled)
                    {
                        Request.CreateErrorResponse(HttpStatusCode.InternalServerError, t.Exception);
                    }
                    string fileName = string.Empty;
                    foreach (MultipartFileData file in provider.FileData)
                    {
                        fileName = file.LocalFileName;
                    }
                    //返回上传后的文件全路径
                    return new HttpResponseMessage() { Content = new StringContent(fileName) };
                });
                return Request.CreateResponse(HttpStatusCode.OK);
            }
            catch (System.Exception e)
            {
                return Request.CreateErrorResponse(HttpStatusCode.InternalServerError, e);
            }
        }

        ///
        /// 重命名上传的文件
        ///
        public class ReNameMultipartFormDataStreamProvider : MultipartFormDataStreamProvider
        {
            public ReNameMultipartFormDataStreamProvider(string root)
                : base(root)
            { }
            public override string GetLocalFileName(System.Net.Http.Headers.HttpContentHeaders headers)
            {
                //截取文件扩展名
                string exp = Path.GetExtension(headers.ContentDisposition.FileName.TrimStart(‘"‘).TrimEnd(‘"‘));
                string name = base.GetLocalFileName(headers);
                return name + exp;
            }
        }

            var temp = ajax.upload("/api/ajaxUpload/upload3/", "#file1", 1024 * 1024 * 1, ["image/png","image/bmp"], function (data) {
                if (data =http://www.mamicode.com/="true") {
                    alert("上传成功！");
                }
                if (data =http://www.mamicode.com/="error") {
                    alert(data);
                }
            });
            console.log(temp);

<form id="formUpload" action="/api/ajaxUpload/upload2/" method="post" enctype="multipart/form-data" target="framFile">
    <input name="isIE8" type="text" value="http://www.mamicode.com/1" readonly style="display: none"/>
    <input id="iefile" type="file" name="age"/>
    <input type="submit" value="http://www.mamicode.com/submit">
</form>
<iframe id="framFile" name="framFile" src="http://www.mamicode.com/postMsg.html"></iframe>