JavaScript: Check a string for palindromes using recursion

JavaScript Function: Exercise-10 with Solution

Recursive Palindrome Check

A palindrome is a word, number, phrase, or other sequence of symbols that reads the same backwards as forwards, such as the words madam or racecar, the date/time stamps 11/11/11 11:11 and 02/02/2020, and the sentence: "A man, a plan, a canal – Panama".
Write a JavaScript program to check whether a given string is a palindrome or not using recursion.

Test Data:
("madam") -> true
("abdb") -> false
("ab") -> false
(test("a") -> true

Sample Solution-1:

JavaScript Code:

// Define a function named 'test' that checks if a given string is a palindrome
const test = (text) => {
  // Check if the input is not a string
  if (typeof text !== 'string') {
    return 'String should not be empty!';
  }

  // Check if the length of the string is less than or equal to 1, it is a palindrome
  if (text.length <= 1) {
    return true;
  }

  // Check if the first and last characters of the string are equal
  if (text[0] !== text[text.length - 1]) {
    return false;
  } else {
    // Recursively call the 'test' function with the string excluding the first and last characters
    return test(text.slice(1, text.length - 1));
  }
};

// Test the 'test' function with different input strings
console.log(test("madam")); // Output: true (palindrome)
console.log(test("abdb"));  // Output: false (not a palindrome)
console.log(test("ab"));    // Output: false (not a palindrome)
console.log(test("a"));     // Output: true (palindrome) 

Output:

true
false
false
true

Flowchart:

Live Demo:

See the Pen javascript-recursion-function-exercise-10 by w3resource (@w3resource) on CodePen.

Sample Solution-2:

JavaScript Code:

// Function to check if a given string is a palindrome using recursion
function isPalindrome(str) {
  // Base case: if the string has 0 or 1 characters, it's a palindrome
  if (str.length <= 1) {
    return true;
  }

  // Check if the first and last characters are equal
  if (str[0] !== str[str.length - 1]) {
    return false;
  } else {
    // Recursively check the substring excluding the first and last characters
    return isPalindrome(str.slice(1, -1));
  }
}

// Test the function with different input strings
console.log(isPalindrome("madam")); // Output: true (palindrome)
console.log(isPalindrome("abdb"));  // Output: false (not a palindrome)
console.log(isPalindrome("ab"));    // Output: false (not a palindrome)
console.log(isPalindrome("a"));     // Output: true (palindrome)

Output:

true
false
false
true

Flowchart:

For more Practice: Solve these Related Problems:

• Write a JavaScript function that recursively checks if a string is a palindrome, ignoring punctuation and case.
• Write a JavaScript function that verifies a palindrome recursively while supporting Unicode characters.
• Write a JavaScript function that uses recursion to check if a string is a palindrome and treats an empty string as true.
• Write a JavaScript function that compares the first and last characters recursively to determine if a string is a palindrome.

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