js下将阿拉伯数字每三位一逗号分隔(如：15000000转化为15,000,000)

"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)