Convert string form RMB

RMB convert a string form, such as 12345678 = "876,543,21

        var strnum = "12345678";
        //实现字符串反转
        function revs(strnum) {
            if (strnum.length > 1) {
                var newstrnum = strnum.split("").reverse().join("");
                return newstrnum;
            }
            return strnum;
        }
        //字符串拼接逗号
        function getRMB(news) {
            var tmp = "";
            for (var i = 1; i <= news.length; i++) {
                tmp += news[i - 1];
                if (i % 3 == 0 && i != news.length) {
                    tmp += ",";
                }
            }
            return tmp;
        }
        var news = revs(strnum);
        console.log(news); //87654321
        var RMB = getRMB(news);
        console.log(RMB);//876,543,21