js數字按千分位逗號分隔

toThousands(num) {
      num = (num || 0).toString();
      let number = 0,
          floatNum = '',
          intNum = '';
      // 判斷是否有小數位，有則截取小數點后的數字
      if (num.indexOf('.') > 0) {
        number = num.indexOf('.'); // 獲取小數點出現的位置
        floatNum = num.substr(number); // 截取arr.substr(form, length)
        intNum = num.substring(0,number); // 截取arr.substring(start, end)
      } else {
        intNum = num;
      }
      let result = [],
          counter = 0;
      intNum = intNum.split('');
      // 利用3的倍數，向數組插入','
      for (let i = intNum.length - 1; i >= 0; i--) {
        counter++;
        result.unshift(intNum[i]);
        if (!(counter % 3) && i != 0) { result.unshift(','); }
      }
      return result.join('') + floatNum || '';
    }