There is a much simpler way to solve this problem and maintain O(n) Time and O(1) space complexity

class Solution {
  isPalindrome(s) {
    s = s.toLowerCase().replace(/[^a-z0-9]/g, '');
    let l = 0;
    let r = s.length - 1;

    while (l < r) {
      if (s[l] !== s[r]) return false
      l++
      r--
    }

return true;

}

}