Largest 3-Same-Digit Number in String LeetCode solution in JavaScript

1
var largestGoodInteger = function (num) {
2
  let maxGoodInt = "";
3
  for (let i = 0; i <= num.length - 3; i++) {
4
    if (num[i] === num[i + 1] && num[i + 1] === num[i + 2]) {
5
      if (num[i] >= maxGoodInt) {
6
        maxGoodInt = num[i];
7
      }
8
    }
9
  }
10
  return maxGoodInt + maxGoodInt + maxGoodInt;
11
};