js数字每3位加一个逗号

if(typeof val ==="number"){
   var str = val.toString();
   var reg = str.indexOf(".") > -1 ? /(\d)(?=(\d{3})+\.)/g : /(\d)(?=(?:\d{3})+$)/g;
   val =  str.replace(reg,"$1,");
   return(
       <div >{val}</div>
   )
}