In this example, you will learn how to check if the string is palindrome or not in JavaScript.

Basically, we are going to learn different ways to checks if the string is palindrome or not in JavaScipt.

A string is a palindrome if it is read the same from forward or backward. For example, dad reads the same either from forward or backward. So the word dad is a palindrome. Similarly, madam is also a palindrome.

JavaScript Checks if the String is Palindrome or not

Two ways to check if String is Palindrome or not:

With built-in functions
With a for loop and straight forward regex

main.js

Let's create a main.js file and add the following code to it:

/* 1. With built in functions
\W matches any non-word character (equal to [^a-zA-Z0-9_])
_ matches the character _ literally (case sensitive)
*/

function isPalindrome(str) {
  return str.replace(/[\W_]/g, '').toLowerCase() ===
         str.replace(/[\W_]/g, '').toLowerCase().split('').reverse().join('');
}

//2. With a for loop and straight forward regex

function isPalindromeUsingLoop(str) {
  var regex = /[^A-Za-z0-9]/g;
  str = str.toLowerCase().replace(regex, '');
  var len = str.length;
  for (var i = 0; i < len/2; i++) {
       if (str[i] !== str[len - 1 - i]) {
           return false;
       }
  }
  return true;
}
 
// testing
console.log(isPalindrome("racecar"));
console.log(isPalindromeUsingLoop("racecar"));

Note that the comments in the above code are self-descriptive.

index.html

To test JavaScript code, let's create an HTML file named index.html and add the following code to it:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <script src="main.js"></script>
</body>
</html>