var iValue = 20002365879; //要转换的数字
var sValue = iValue+'';
var aValue = new Array();
var iNum = sValue.length%3;
var aResult; //转换结果
var index = 0;
if(sValue.length<=3){
 console.log(sValue);
}else{
 if(iNum == 0){
 for(var i=0; i<sValue.length; i=i+3){
  aValue[index] = sValue[i]+''+sValue[i+1]+''+sValue[i+2];
  index++;
 }
}else if(iNum == 1){
 aValue[0] = sValue[0];
 index = 1;
 for(var i=1; i<sValue.length; i=i+3){
  aValue[index] = sValue[i]+''+sValue[i+1]+''+sValue[i+2];
  index++;
 }
}else if(iNum == 2){
 aValue[0] = sValue[0]+''+sValue[1];
 index = 1;
 for(var i=2; i<sValue.length; i=i+3){
  aValue[index] = sValue[i]+''+sValue[i+1]+''+sValue[i+2];
  index++;
 }
}
aResult = aValue.join(',');
console.log(aResult.toString());//输出20,002,365,879
}