在Javascript中转换为罗马数字 - 奇怪的错误

function convertToRoman(num) {

  var thisMap = {

  1:[1],
  2:[1, 1],
  3:[1, 1, 1],
  4:[1, 5],
  5:[5],
  6:[5, 1],
  7:[5, 1, 1],
  8:[5, 1, 1, 1],
  9:[1, 10],
  0:[0]

  };

  var numMap = {

  1000:"M",
  500:"D",
  100:"C",
  50:"L",
  10:"X",
  5:"V",
  1:"I"

  };

  numArr = num.toString().split("");

  var thisIndex = 1;

  var tallyArr = [];

  for (var i = numArr.length - 1; i >= 0; i--) {

   tallyArr.unshift(thisMap[numArr[i]]);

  }

  thisIndex = Math.pow(10, tallyArr.length - 1);

  checkArr = [];

  <<<BUG HERE>>> 

  for (var x = 0; x < tallyArr.length; x++) {

    for (var y = 0; y < tallyArr[x].length; y++) {

      tallyArr[x][y] *= thisIndex;

    }

    thisIndex = thisIndex / 10;

  }

  <<</BUG HERE>>>

  var finalArr = [];

  for (var a = 0; a < tallyArr.length; a++) {

    for (var b = 0; b < tallyArr[a].length; b++) {

      finalArr.push(numMap[tallyArr[a][b]]);

    }

  }

  finalAnswer = finalArr.join("");

  return finalAnswer;

}

convertToRoman(88);
function convertToRoman(num) {

  var thisMap =