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);
}