javascript整数千分位格式化函数

    function formatNum(str) {
        var newStr = "";
        var count = 0;
        if (str.indexOf(".") == -1) {
            for (var i = str.length - 1; i >= 0; i--) {
                if (count % 3 == 0 && count != 0) {
                    newStr = str.charAt(i) + "," + newStr;
                } else {
                    newStr = str.charAt(i) + newStr;
                }
                count++;
            }
            str = newStr;
            return str;
        }
    }
   var n = formatNum("1453153");
    console.log(n);

    function formatNum(val) {
        var newStr = "";
        var count = 0;
        var str = val.split(".")[0];
        if (str.indexOf(".") == -1) {
            for (var i = str.length - 1; i >= 0; i--) {
                if (count % 3 == 0 && count != 0) {
                    newStr = str.charAt(i) + "," + newStr;
                } else {
                    newStr = str.charAt(i) + newStr;
                }
                count++;
            }
            str = newStr + "." + val.split(".")[1];
            return str;
        }
    }
    var n = formatNum("1453105453.1231");
    console.log(n);