JS 四舍五入 自定义小数位数，空缺补0

function formatnumber(value, num){
     var a, b, c, i;
     a = value.toString();
     b = a.indexOf(".");
     c = a.length;
     if (num == 0) {
         if (b != -1) {
             a = a.substring(0, b);
         }
     } else {
         if (b == -1) {
             a = a + ".";
             for (i = 1; i <= num; i++) {
                 a = a + "0";
             }
         } else {
             a = a.substring(0, b + num + 1);
             for (i = c; i <= b + num; i++) {
                 a = a + "0";
             }
         }
     }
     return a;
 }

//public cyj
//对数字进行四舍五入计算
function round(num,n)...{
 var   dd=1; 
 var   tempnum; 
 for(i=0;i<n;i++)...{ 
 dd*=10; 
 } 
 tempnum=num*dd; 
 tempnum=Math.round(tempnum);
 return formatnumber(tempnum/dd,n); 
}