formatNum(num) {
  if (num > 99 || num < 1) {
    throw new Error("僅支援格式化100以內的正整數");
  }
  var gewei = num % 10;
  var str;
  if (gewei == 0) {
    str = '十';
  } else {
    str = this.numArray[gewei-1];
  }
  if (num > 10) {
    var shiwei = Math.floor(num / 10);
    if (gewei == 0) {
      str = this.numArray[shiwei-1] + str;
    } else if (shiwei == 1) {
      str = '十' + str;
    } else {
      str = this.numArray[shiwei-1] + '十' + str;
    }
  }
  return str;
},