js将金额等类型数值每隔三位用逗号分隔

function toThousands(num){
      let result = '', counter = 0;
      let dot = String(num).indexOf(".");
      if (dot != -1) {
        // alert("有小数点");
        // 获取小数点后面的数字(indexOf和substring都不支持数字，所以要先转字符串才可以用)
        let dotCnt = String(num).substring(dot + 1, num.length);

        // 获取小数点前面的数字
        num = String(num).split('.')[0]
        num = (num || 0).toString();
        for (var i = num.length - 1; i >= 0; i--) {
          counter++;
          result = num.charAt(i) + result;
          if (!(counter % 3) && i != 0) {
            result = ',' + result;
          }
        }
        result = result + '.' + dotCnt;
        return result;

      } else {
        // alert("没有小数点");
        return (num || 0).toString().replace(/(\d)(?=(?:\d{3})+$)/g, '$1,');
      }
    }