写一个方法判断字符串是否为回文字符串

/**
 * Checks if a given string is a palindrome.
 *
 * @param {string} str The string to check.
 * @param {boolean} [caseSensitive=false] Whether the comparison should be case-sensitive.
 * @returns {boolean} True if the string is a palindrome, false otherwise.
 */
function isPalindrome(str, caseSensitive = false) {
  if (!str) {
    return true; // Empty string is considered a palindrome
  }

  const processedStr = caseSensitive ? str : str.toLowerCase();
  const reversedStr = processedStr.split('').reverse().join('');

  return processedStr === reversedStr;
}


// Examples
console.log(isPalindrome("racecar")); // true
console.log(isPalindrome("Racecar")); // false (case-sensitive by default)
console.log(isPalindrome("Racecar", true)); // false (case-sensitive)
console.log(isPalindrome("Racecar", false)); // true (case-insensitive)
console.log(isPalindrome("A man, a plan, a canal: Panama", false)); // true (ignores non-alphanumeric characters and case)
console.log(isPalindrome("")); // true (empty string)
console.log(isPalindrome(null)); // true (null/undefined treated as empty string)


/**
 * More robust version handling non-alphanumeric characters.
 *
 * @param {string} str The string to check.
 * @param {boolean} [caseSensitive=false] Whether the comparison should be case-sensitive.
 * @returns {boolean} True if the string is a palindrome, false otherwise.
 */
function isPalindromeRobust(str, caseSensitive = false) {
  if (!str) {
    return true; // Empty string is considered a palindrome
  }

  const alphanumericStr = str.replace(/[^a-zA-Z0-9]/g, ''); // remove non-alphanumeric chars
  const processedStr = caseSensitive ? alphanumericStr : alphanumericStr.toLowerCase();

  let left = 0;
  let right = processedStr.length - 1;

  while (left < right) {
    if (processedStr[left] !== processedStr[right]) {
      return false;
    }
    left++;
    right--;
  }

  return true;
}



// Robust examples
console.log(isPalindromeRobust("A man, a plan, a canal: Panama")); // true
console.log(isPalindromeRobust("Race car!")); // true
console.log(isPalindromeRobust("Was it a car or a cat I saw?")); // true
console.log(isPalindromeRobust("hello")); // false

This code provides two functions:

• isPalindrome(str, caseSensitive): A basic palindrome checker. It's concise but doesn't handle non-alphanumeric characters well. The caseSensitive parameter lets you control whether case matters.

• isPalindromeRobust(str, caseSensitive): A more robust version that removes non-alphanumeric characters before checking. This is generally more useful for real-world scenarios. It also uses a two-pointer approach which is generally more efficient than reversing the entire string.

Both functions treat empty strings (and null/undefined) as palindromes. The examples demonstrate how to use them and the differences in their behavior. I've included comments to explain the code clearly. Choose the function that best suits your needs.