用js实现千位分隔符

用js实现千位分隔符，适用于金额展示（正则+replace）

 function commafy(num) {
        return num && num
            .toString()
            .replace(/(\d)(?=(\d{3})+\.)/g, function($0, $1) {
                return $1 + ",";
            });
    }
 console.log(commafy(1312567.903000));

结果：1,312,567.903