判断execl格式

function dianji() {
/* var myselect=document.getElementById("select");
var index=myselect.selectedIndex;
var e= myselect.options[index].value;
alert(e);*/
var u= document.getElementById("image_file").value;

//var reg = /^.*\.(?:xls|xlsx)$/i;
//判断是否是execl
var ext = u.slice(u.lastIndexOf(".")+1).toLowerCase();
if(u==''||ext!="xlsx")
{
alert("请选择xlsx文件,谢谢");
window.location.href="http://localhost:8080/SSM/index.html";
}else if(u!=''){
$("#upload_form").submit();
}


}