清空上传控件的值

var form=document.createElement('form');
                                    document.body.appendChild(form);
                                    var pos=$("#FileUpload1").get(0).nextSibling;
                                    form.appendChild($("#FileUpload1").get(0));
                                    form.reset();
                                    pos.parentNode.insertBefore($("#FileUpload1").get(0),pos);
                                    document.body.removeChild(form);