JS中千分位的处理

function commafy(num) {
                    //1.先去除空格,判断是否空值和非数
                    num = num + "";
                    num = num.replace(/[ ]/g, ""); //去除空格
                    if (num == "") {
                    return;
                    }
                    if (isNaN(num)){
                    return;
                    }
                    //2.针对是否有小数点，分情况处理
                    var index = num.indexOf(".");
                    if (index==-1) {//无小数点
                      var reg = /(-?\d+)(\d{3})/;
                        while (reg.test(num)) {
                        num = num.replace(reg, "$1,$2");
                        }
                    } else {
                        var intPart = num.substring(0, index);
                        var pointPart = num.substring(index + 1, num.length);
                        var reg = /(-?\d+)(\d{3})/;
                        while (reg.test(intPart)) {
                        intPart = intPart.replace(reg, "$1,$2");
                        }
                       num = intPart +"."+ pointPart;
                    }
                return num;
                }