js校验上传文件的格式

<%@ page language="java" i++mport="java.uti++l.*" pageEncoding="UTF-8"%>
<%@ taglib prefix="j" uri="http://java.sun.com/jsp/jstl/core"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="https://blog.51cto.com/u_15446828/4774702/<%=basePath%>">

<title>My JSP 'index.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="https://blog.51cto.com/u_15446828/4774702/styles.css">
-->
<script type="text/javascript">
function validateFileType(){
var obj = document.getElementById("files");
if(obj.value == "" || obj.value == null){
alert("请选择上传文件!");
return ;
}
//获取文件的后缀名的位置
var index = obj.value.lastIndexOf(".");
if(index == -1){
alert("上传文件类型不对!");
return;
}
//截取后缀名
var type = obj.value.substring(index+1);
if(type != "jpg" && type != "png" && type != "jpeg"){
alert("请选择图片文件上传!");
return;
}else{
alert("您对了!");
}
}
</script>
</head>

<body>
<h1>校验上传文件类型</h1>

<form action="" >
<input type="file" name="files" id="files" value="" ></input>
<input type="button" nclick="validateFileType()" name="" value="测试">
</form>

</body>
</html>