num为传入的数字,n为保留几位小数

fomatFloat(num, n) {
      let f = parseFloat(num);
      if (isNaN(f)) {
        return false;
      }
      f = Math.round(num * Math.pow(10, n)) / Math.pow(10, n); // n 幂   
      let s = f.toString();
      let rs = s.indexOf('.');
      //判定如果是整数，增加小数点再补0
      if (rs < 0) {
        rs = s.length;
        s += '.';
      }
      while (s.length <= rs + n) {
        s += '0';
      }
      return s;
    }
console.log(this.fomatFloat(232.65, 2));//232.65