如何高效获取尾部字符串

 1 <script type="text/javascript">
 2         var  getString=function(fileName){
 3                 return fileName.split(".").pop();
 4         }
 5         //例1
 6         var fileName1 = "photo.jpg";
 7         var getString1 = getString(fileName1);    // 获取值 jpg
 8         alert(getString1);
 9 
10         //例2
11         var fileName2 = "main.js";
12         var getString2 = getString(fileName2);   // 获取值 js
13         alert(getString2);
14     </script>