限制提交图片格式

var uploadpath = document.getElementById(‘uploadpath‘);
var simplepath = uploadpath.innerText;
var pathsuffix = simplepath.substr(simplepath.lastIndexOf(‘.‘));
//通过正则表达式判断是否为相关后缀
if (/\.(gif|jpg|jpeg|bmp|png)$/.test(pathsuffix))
　　alert("请选择正确格式图片:gif,jpg,jpeg,bmp,png");

//获取文件
var file = this.Request.Form.Files["uploadpayimage"];
//截取文件后缀
var fileSuffix= file.FileName.Substring(file.FileName.LastIndexOf(".") + 1)
//根据枚举内容判断是否是图片后缀
if(!Enum.IsDefined(typeof(ImageType), fileSuffix)){
    return false;
}

//枚举类
public enum ImageType
{
    jpg = 0,
    jpeg = 1,
    png = 2,
    gif = 3,
    bmp = 4
}

var file = this.Request.Form.Files["uploadpayimage"];
//获取文件类型
var fileType = file.ContentType.Substring(0, file.ContentType.LastIndexOf("/"));
if(!fileType.Equals("image"))
{
    return false;
}