js 数字添加逗号，格式化数字

      function addCommas(nStr)
        {
            nStr += '';
            x = nStr.split('.');
            x1 = x[0];
            x2 = x.length > 1 ? '.' + x[1] : '';
            var rgx = /(\d+)(\d{3})/;
            while (rgx.test(x1)) {
                x1 = x1.replace(rgx, '$1' + ',' + '$2');
            }
            return x1 + x2;
        }

//数字格式化就可以变成
      var num = 123456.4231;
          num = num.toFixed(2);
          num =addCommas(num);
//     num = 123456.42