js格式化金额可选是否带千分位以及保留精度

/* 
将数值四舍五入后格式化. 
@param num 数值(Number或者String) 
@param cent 要保留的小数位(Number) 
@param isThousand 是否需要千分位 0:不需要,1:需要(数值类型); 
@return 格式的字符串,如'1,234,567.45' 
@type String 
*/ 
function formatNumber(num,cent,isThousand){ 
num = num.toString().replace(/\$|\,/g,''); 
if(isNaN(num))//检查传入数值为数值类型. 
num = "0"; 
if(isNaN(cent))//确保传入小数位为数值型数值. 
cent = 0; 
cent = parseInt(cent); 
cent = Math.abs(cent);//求出小数位数,确保为正整数. 
if(isNaN(isThousand))//确保传入是否需要千分位为数值类型. 
isThousand = 0; 
isThousand = parseInt(isThousand); 
if(isThousand < 0) 
isThousand = 0; 
if(isThousand >=1) //确保传入的数值只为0或1 
isThousand = 1; 
sign = (num == (num = Math.abs(num)));//获取符号(正/负数) 
//Math.floor:返回小于等于其数值参数的最大整数 
num = Math.floor(num*Math.pow(10,cent)+0.50000000001);//把指定的小数位先转换成整数.多余的小数位四舍五入. 
cents = num%Math.pow(10,cent); //求出小数位数值. 
num = Math.floor(num/Math.pow(10,cent)).toString();//求出整数位数值. 
cents = cents.toString();//把小数位转换成字符串,以便求小数位长度. 
while(cents.length<cent){//补足小数位到指定的位数. 
cents = "0" + cents; 
} 
if(isThousand == 0) //不需要千分位符. 
return (((sign)?'':'-') + num + '.' + cents); 
//对整数部分进行千分位格式化. 
for (var i = 0; i < Math.floor((num.length-(1+i))/3); i++) 
num = num.substring(0,num.length-(4*i+3))+','+ 
num.substring(num.length-(4*i+3)); 
return (((sign)?'':'-') + num + '.' + cents); 
}