"15000000".split("").reverse().join("").replace(/(\d{3})/g, "$1,").split("").reverse().join("");

"115000000".split("").reverse().join("").replace(/(\d{3})(?=[^$])/g, "$1,").split("").reverse().join("");

var cutStr = function(str){  var newStr= new Array(str.length+ parseInt(str.length/3));   newStr[newStr.length-1]=str[str.length-1];   var currentIndex=str.length-1;   for(var i = newStr.length-1;i >= 0;i--)   {     if((newStr.length-i)%4==0)     {       newStr[i]=",";     }    else    {       newStr[i]=str[currentIndex--];     }   }   return newStr.join("") } var num="15000000";console.log(cutStr(num));

function cutStr(str){    var rmb='';    var i2=0;    for(var i=str.length-1; i>=0; i--){        if(i%3==0&&i!=0){            rmb+=str[i2]+',';        }else{            rmb+=str[i2];        }        i2++;    }    return rmb;}console.log(cutStr(num));

function cutStr(num) {    var aaa = num.toString();    var arr1 = aaa.split("");    var arr2 = [];    for (var i = 0; i < arr1.length;) {        for (j = 0; j < 3; j++) {            arr2.unshift(arr1[i]);            i++;            if (j == 2 && i < arr1.length) {                arr2.unshift(",");            }        }    }    alert(arr2.join(""));}cutStr(12345678);

'1500000000000'.replace(/\B(?=(\d{3})+$)/g,',')

function formatNumber(value) {    value = value.toString();    if (value.length <= 3) {        return value;    } else {        return formatNumber(value.substr(0, value.length - 3)) + ',' + value.substr(value.length - 3);    }}console.log(formatNumber(12345678))

var str = '123123211312.333123'.replace(/(?=(?!^)(?:\d{3})+(?:\.|$))(\d{3}(\.\d+$)?)/g,',$1');console.log(str)