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