js 四捨五入函數

<script language="javascript"> 
document.write("<h1>JS保留兩位小數例子</h1><br>");  
   var a=2.1512131231231321;  
   document.write("原來的值："+a+"<br>");  
   document.write("兩位小數點:"+a.toFixed(2)+"<br>四位小數點"+a.toFixed(4));  
</script>