JS数字格式化

JS实现数字格式化输出，比如输入999999999，输出9,999,999,999

splitNum:function(n){    
  var b=parseInt(n).toString();
  var len=b.length;    
  if(len<=3){return b;}    
  var r=len%3;    
  return r>0?b.slice(0,r)+","+b.slice(r,len).match(/\d{3}/g).join(","):b.slice(r,len).match(/\d{3}/g).join(",");
}