Longest Palindromic Substring.js

const isPalindromic = (s) => {
  const center = Math.floor(s.length / 2);
  for(let i = 0; i <= center; i += 1) {
    if(s[i] !== s[s.length - 1 - i]) {
      return false;
    }
  }
  return true;
}

const findLastSameStringIndex = (string, target, lastIndex) => {
  for(let i = lastIndex - 1; i >= 0; i -= 1) {
    if (target === string[i]) {
      return i;
    }
  }
}

var longestPalindrome = function(s) {
  if (s === '') return '';
  let answer = s[0];

  for (let i = 0; i < s.length; i+= 1) {
    let lastSameStrIndex = findLastSameStringIndex(s, s[i], s.length);

    while(lastSameStrIndex !== i) {
      const currentStr = s.slice(i, lastSameStrIndex + 1);

      if (currentStr.length <= answer.length) break;

      if (isPalindromic(currentStr)) {
        answer = currentStr;
        break;
      }

      lastSameStrIndex = findLastSameStringIndex(s, s[i], lastSameStrIndex);
    }
  }
  return answer;
};