Highest Value Palindrome

function maximumPalinUsingKChanges(str, k) {
  let palin = str.split("");
  let ans = "";

  let l = 0;
  let r = str.length - 1;
  let changedArray = [];

  while (l < r) {
    if (str[l] != str[r]) {
      palin[l] = palin[r] = Math.max(str[l], str[r]);
      changedArray[l] = true;
      k--;
    }
    l++;
    r--;
  }

  if (k < 0) {
    return "Not possible";
  }

  l = 0;
  r = str.length - 1;

  while (l <= r) {
    if (palin[l] !== 9) {
      if (changedArray[l] && k > 0) {
        palin[l] = palin[r] = "9";
        k--;
      } else if (!changedArray[l] && k >= 2) {
        palin[l] = palin[r] = "9";
        k = k - 2;
      }
    }
    if ((l === r) & (k > 0)) {
      palin[l] = "9";
    }
    l++;
    r--;
  }
  for (let i = 0; i < palin.length; i++) ans += palin[i];
  return ans;
}

let str = "3493";

console.log(str.length);
let k = 1;
console.log(maximumPalinUsingKChanges(str, k));