JS格式化数字成逗号分隔&JS四舍五入

//将数字格式化成逗号分隔的形式
function  formatSplitNum(num)
{   
    if(!/^(\+|-)?(\d+)(\.\d+)?$/.test(num)){
        return   num;
    }   
    var   a   =   RegExp.$1,   b   =   RegExp.$2,   c   =   RegExp.$3;   
    var   re   =   new   RegExp().compile("(\\d)(\\d{3})(,|$)");   
    while(re.test(b))   b   =   b.replace(re,   "$1,$2$3");   
    return   a   +""+   b   +""+   c;   
}

//四舍五入函数
new Number(sumValue).toFixed(precision);