js正则表达式判断ip格式

       //判断IP地址是否合法
       function checkIP()
       {
         var obj =document.forms[0].save_operateIp.value;
         var exp=/^(\d{1,2}|1\d\d|2[0-4]\d|25[0-5])\.(\d{1,2}|1\d\d|2[0-4]\d|25[0-5])\.(\d{1,2}|1\d\d|2[0-4]\d|25[0-5])\.(\d{1,2}|1\d\d|2[0-4]\d|25[0-5])$/;
         var reg = obj.match(exp);
         if(reg==null)
         {
           return
false;
         }
         else
         {
          return
true;
         }
       }