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;   
                }