function amount(s,n) {

            // s amount   n  保留的小数位数

            if(n===undefined)
                n=2;

            s = parseFloat((s + "").replace(/[^\d\.-]/g, "")).toFixed(n) + "";

            var l = s.split(".")[0].split("").reverse(), r = s.split(".")[1], t = "";

            for (var i = 0; i < l.length; i++) {

                t += l[i] + ((i + 1) % 3 == 0 && (i + 1) != l.length ? "," : "");
            }
            
            var res=t.split("").reverse().join("");
            
            if(n==0)
                return res;
            
            return res + "." + r;
        }

        amount(321321,2)  // 321,321.20