Linear-ish time solution for finding longest palindrome in string.

longestPalindrome

var longestPalindrome = function (string) {
  var current, i, isPalindrome, j, longest;

  longest = current = '';

  for (i = string.length - 2; i >= 0; i--) {
    j = 1;

    do {
      // check for odd palindrome
      if (string[i - j] === string[i + j] && string[i - j]) {
        isPalindrome = true;

        current = string.substring(i - j, i + j + 1);

        j++;
      // check for even palindrome
      } else if (string[i - j + 1] === string[i + j] && string[i - j + 1]) {
        isPalindrome = true;

        current = string.substring(i - j + 1, i + j + 1);

        j++;
      // compare length of current and longest
      } else {
        isPalindrome = false;

        if (current.length > longest.length) longest = current;
      }
    } while (isPalindrome);
  }

  return longest;
};