html5 ajax 跨域上传图片

html:

            <div class="w-img choseimg">
                <input type="file">
                <img src="" id="imageId">
            </div>

js:

// 读取地址
        function readURL(input, tmpimg) {

            if (input.files && input.files[0]) {
                var reader = new FileReader();

                reader.onload = function (e) {
                    if (!/image/.test(e.target.result)) {
                        alert('请上传图片格式...');
                        return false;
                        alert(22);
                    }
                    tmpimg.attr('src', e.target.result);
                }
                reader.readAsDataURL(input.files[0]);
            }
        }
        var stringImg = "";
        $(function () {
            // var tmpimgurl = $(".choseimg img").attr('src');
            // 头像
            $(".choseimg input").change(function () {
                var $me = $(this);
                var $img = $me.parent().find('img');
                readURL(this, $img);

                var file = this.files[0];
                var formData = new FormData();
                formData.append('img1', file);
               $.ajax({
                    type: "POST", //必须用post
                    url: "http://<%=maindomain %>/MicroMartApi/MemberHandler.ashx?action=upload&username=" + username.username,
                    crossDomain: true,
                    jsonp: "jsoncallback",
                    data: formData,
                    contentType: false, //必须
                    processData: false,
                    //不能用success，否则不执行
                    complete: function (data) {
                        var data = eval(data.responseText);
                        console.log(data.Data);
                    }
                });
            });

        });

后台：

 /// <summary>
        /// 支持跨域请求
        /// </summary>
        /// <param name="context"></param>
        public static void Origin()
        {
            string callBackName = HttpContext.Current.Request.Params["jsoncallback"] == null ? "" : HttpContext.Current.Request.Params["jsoncallback"].ToString();
            if (string.IsNullOrEmpty(callBackName))     //此参数如果为空，则表示客户端使用的不是jsonp方式的ajax请求
            {
                HttpContext.Current.Response.ClearHeaders();
                string origin = HttpContext.Current.Request.Headers["Origin"];
                HttpContext.Current.Response.AppendHeader("Access-Control-Allow-Origin", string.IsNullOrEmpty(origin) ? "*" : origin);
                string requestHeaders = HttpContext.Current.Request.Headers["Access-Control-Request-Headers"];
                HttpContext.Current.Response.AppendHeader("Access-Control-Allow-Headers", string.IsNullOrEmpty(requestHeaders) ? "*" : requestHeaders);
                HttpContext.Current.Response.AppendHeader("Access-Control-Allow-Methods", "POST, OPTIONS");
            }
        }

        /// <summary>
        /// ajax请求返回数据
        /// </summary>
        /// <param name="jsonData"></param>
        public static void AjaxWrite(string jsonData)
        {
            HttpContext.Current.Response.ContentType = "application/json;charset=utf-8";
            string callBackName = string.Empty;
            callBackName = HttpContext.Current.Request.Params["jsoncallback"] == null ? "" : HttpContext.Current.Request.Params["jsoncallback"].ToString();
            if (!string.IsNullOrEmpty(callBackName))         //此参数如果为空，则表示客户端使用的不是jsonp方式的ajax请求
            {
                HttpContext.Current.Response.Write(callBackName + "("+jsonData+")");
            }
            else
            {
                HttpContext.Current.Response.Write(jsonData);
            }
        }


protected void Page_Load(object sender, EventArgs e)
        {
            Response.Clear();
            WebFormHandler.Origin();
            string Action=Request["Action"];
            switch (Action) {
                case "QueryRelation":
                    QueryRelation();
                    break;
                case "QueryManageRelation":
                    QueryManageMember();
                    break;
                case "RetailAwardTrace":
                    RetailAwardTrace();
                    break;
                case "RetailAwardQuery":
                    RetailAwardQuery();
                    break;
                case "StockAwardTrace":
                    StockAwardTrace();
                    break;
                case "StockAwardQuery":
                    StockAwardQuery();
                    break;
            }
            WebFormHandler.AjaxWrite("(" + json + ")");
            Response.End();
        }