数字加千位符

代码：

/**
  * @param {Number} num - 数字.
*/
 addSymbol(num){
   let res=num.toString().replace(/\d+/, function(n){
       return n.replace(/(\d)(?=(\d{3})+$)/g,function($1){
           return $1+",";
       });
   })
   return res;
 },