var fileName = "http://www.111cn.net/sys/nginx/62888.htm";方法1

var fileExtension = fileName.substring(fileName.lastIndexOf('.') + 1);

或者 var strtype=strFileName.substring(strFileName.length-3,strFileName.length);

strtype=strtype.toLowerCase();

方法2

var fileExtension = fileName.split('.').pop().toLowerCase();

方法3

var str=document.getElementById("FileUpload1").value; var pos = str.lastIndexOf("."); var lastname = str.substring(pos,str.length)