April 8, 2022

How to Check if a String is Palindrome in Javascript

By Krishnaa JavaScript Questions 0 Comments

In this tutorial, you will learn how to check if a string is palindrome in javascript. A palindrome is a word, sentence, or number which reads the same backward as well as forward such as level, madam, refer, 1881, etc. If you write 1881 in English words, it will be one thousand eight hundred and eighty-one. It will remain the same even if you write that number in reverse order.

There are numerous ways to check if a string is palindrome. We are going to use one of the easiest solutions which involve the usage of the Array.from() method, reverse() method, join() method, and ternary (?) operator.

The Array.from() method returns an array from any object that has a length property. The reverse() method reverses the order of items in an array. The join() method converts an array into a string. It also takes a separator as a parameter, but it is optional. The default separator is a comma (,). The ternary operator is also known as the conditional operator which acts similar to the if-else statement.

In the following example, we have one global variable and upon click of a button, we will check if the string is a palindrome and display the result on the screen. Please have a look over the code example and the steps given below.

HTML & CSS

We have 3 elements in the HTML file (div, button, and h1). The div element is just a wrapper for the rest of the elements.
The innerText for the button element is “Check” and for the h1 element, it is “Result”.
We have done some basic styling using CSS and added the link to our style.css stylesheet inside the head element.
We have also included our javascript file script.js with a script tag at the bottom.

<!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">
  <link rel="stylesheet" href="style.css">
  <title>Document</title>
</head>

<body>

  <div class="container">    
    <button>Check</button>
    <h1>Result</h1>
  </div>

  <script src="script.js"></script>
</body>

</html>

.container {        
    text-align: center;
}

button {
  margin-top: 10px;
  padding: 10px 20px;
}

Javascript

We have selected the button element and h1 element using the document.querySelector() method and stored them in btnCheck and output variables respectively.
We have attached a click event listener to the button element.
We have a global variable myVar which holds a palindrome string as its value.
In the event handler function, we are calling the isPalindrome() method and passing myVar as a parameter. This method will check if a string is a palindrome and return a Boolean value.
In the isPalindrome() method, we are converting the string to an array of characters using the Array.from() method, reversing the array using the reverse() method, and converting it back to a string using the join() method. The returned string is stored in the reverseStr variable.
We are using the strict equality operator (===) to check whether the original string and reversed string are equal. This check will give us a Boolean value and we will simply return it.
Depending upon the result of the check, we will assign “Yes” or “No” to the result variable.
We are displaying the result in the h1 element using the innerText property.

let btnCheck = document.querySelector("button");
let output = document.querySelector("h1");

let myVar = "radar";

btnCheck.addEventListener("click", () => {
  let result = isPalindrome(myVar) ? "Yes" : "No";
  output.innerText = result;
});

function isPalindrome(str) {
  let reverseStr = Array.from(str).reverse().join("");
  return str === reverseStr;
}

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