javascript如何获取文件的后缀格式

//by MoreWindows (http://www.51texiao.cn/)  
function GetExtensionFileName(pathfilename) 
{ 
    var reg = /(\\+)/g; 
    var pfn = pathfilename.replace(reg, "#"); 
    var arrpfn = pfn.split("#"); 
    var fn = arrpfn[arrpfn.length - 1]; 
    var arrfn = fn.split("."); 
    return arrfn[arrfn.length - 1]; 
} 
//by MoreWindows (http://www.51texiao.cn/)
function GetExtensionFileName(pathfilename)
{
 var reg = /(\\+)/g;
 var pfn = pathfilename.replace(reg, "#");
 var arrpfn = pfn.split("#");
 var fn = arrpfn[arrpfn.length - 1];
 var arrfn = fn.split(".");
 return arrfn[arrfn.length - 1];
}