palindrome.js

function palindrome(word) {
  if (word.length < 2) return true;

  const lastIndex = word.length - 1;
  const indexBeforeLast = word.length - 2;

  return word[0] == word[lastIndex] && palindrome(word.substr(1, indexBeforeLast));
}

console.log("empty:", palindrome(""));
console.log("a:", palindrome("a"));
console.log("aa:", palindrome("aa"));
console.log("ab:", palindrome("ab"));
console.log("abb:", palindrome("abb"));
console.log("aba:", palindrome("aba"));
console.log("abba:", palindrome("abba"));
console.log("abaa:", palindrome("abaa"));
console.log("abcdedcba", palindrome("abcdedcba"));
console.log("abcdeecba", palindrome("abcdeecba"));