input file post文件上传加预览

//html
<input id="fileUpload" type="file" class="fileup" name="file" />
<img src="i.jpg"/>
//js
<script>
 $("#fileUpload").on('change', function () {

        //获取上传文件的数量
        var countFiles = $(this)[0].files.length;
       
        var files = $(this)[0].files[0];
        var imgPath = $(this)[0].value;
        var extn = imgPath.substring(imgPath.lastIndexOf('.') + 1).toLowerCase();
        var image_holder = $("#imageholder");
        image_holder.empty();

        if (extn == "gif" || extn == "png" || extn == "jpg" || extn == "jpeg") {
            if (typeof (FileReader) != "undefined") {

                // 循环全部要上传的图片
                for (var i = 0; i < countFiles; i++) {

                    var reader = new FileReader();
                  
                    reader.onload = function (e) {
                       
                        $("<img />", {
                            "src": e.target.result,
                            "class": "thumb-image"
                        }).appendTo(image_holder);
                     
                    }

                    image_holder.show();
                    reader.readAsDataURL($(this)[0].files[i]);
                    var formdata_file = new FormData();
                    formdata_file.append("file", files);
                $.ajax({
                    type: 'post',
                      url: filesUrl + 'ImageHelper/UpLoadLogo?upload=file',
                      data: formdata_file,
                      processData: false,
                      contentType: false,
                      dataType: "json",
                            success: function (response) {
                                console.log(response.data.src);
                                self.me().logo = response.data.src;
                              }
                })
                 }
               

            } else {
                alert("你的浏览器不支持FileReader！");
            }
        } else {
            alert("请选择图像文件。");
        }
    });


</script>

图片采用post上传，实例化表单对象new FormData()，添加上传后的图片append("file", files)，post添加processData: false,contentType: false,图片预览渲染采用FileReader()，reader.readAsDataURL($(this)[0].files[i])。