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Examples

Palindrome Program in JavaScript (5 Ways)

A palindrome is a word, number, phrase, or sequence of characters that reads the same backward as forward. Examples include:

  • Palindrome strings: "madam", "radar", "level".

  • Palindrome numbers: 121, 1331, 12321.

This program tutorial demonstrates how to write a JavaScript program for palindrome checks, covering strings, numbers, and case-insensitive comparisons.

Palindrome Check for a String in JavaScript

This program checks if a given string is a palindrome by reversing it and comparing it to the original.

Code

function isPalindromeString(str) {
    const reversed = str.split('').reverse().join('');
    return str === reversed;
}

// Test the function
const testString = "madam";
console.log(`Is '${testString}' a palindrome?`, isPalindromeString(testString));

Output

Is 'madam' a palindrome? true

Explanation

  • The split method splits the string into an array of characters.

  • The reverse method reverses the array.

  • The join method converts the array back into a string for comparison.

Palindrome Check for a Number in JavaScript

This program checks if a given number is a palindrome by reversing its digits and comparing it to the original number.

Code

function isPalindromeNumber(num) {
    const strNum = num.toString();
    const reversed = strNum.split('').reverse().join('');
    return strNum === reversed;
}

// Test the function
const testNumber = 121;
console.log(`Is ${testNumber} a palindrome?`, isPalindromeNumber(testNumber));

Output

Is 121 a palindrome? true

Explanation

  • The number is converted to a string using toString().

  • The same reversal logic as the string palindrome check is applied.

JavaScript Program to Check Palindrome Using Built-in Functions

This program demonstrates a concise way to check for palindromes using JavaScript’s built-in methods.

Code

function isPalindromeUsingBuiltIn(input) {
    const str = input.toString().toLowerCase();
    return str === [...str].reverse().join('');
}

// Test the function
const testInput = "Radar";
console.log(`Is '${testInput}' a palindrome?`, isPalindromeUsingBuiltIn(testInput));

Output

Is 'Radar' a palindrome? true

Explanation

  • The input is converted to a lowercase string to ensure case-insensitive comparison.

  • The spread operator (...) creates an array for reversal and joining.

JavaScript Program to Check Palindrome Using For Loop

This program uses a for loop to check for palindromes by comparing characters from the start and end of the string.

Code

function isPalindromeUsingForLoop(str) {
    const len = str.length;
    for (let i = 0; i < len / 2; i++) {
        if (str[i] !== str[len - 1 - i]) {
            return false;
        }
    }
    return true;
}

// Test the function
const loopTestString = "level";
console.log(`Is '${loopTestString}' a palindrome?`, isPalindromeUsingForLoop(loopTestString));

Output

Is 'level' a palindrome? true

Explanation

  • The for loop compares the characters at the start and end of the string, moving towards the center.

  • If a mismatch is found, the function returns false; otherwise, it returns true.

Case-Insensitive Palindrome Check in JavaScript

This program performs a case-insensitive comparison by converting the string to lowercase before checking.

Code

function isCaseInsensitivePalindrome(str) {
    const normalized = str.toLowerCase();
    const reversed = normalized.split('').reverse().join('');
    return normalized === reversed;
}

// Test the function
const caseInsensitiveString = "Level";
console.log(`Is '${caseInsensitiveString}' a palindrome?`, isCaseInsensitivePalindrome(caseInsensitiveString));

Output

Is 'Level' a palindrome? true

Explanation

  • The toLowerCase() method ensures that comparisons are case-insensitive.

  • The rest of the logic is similar to the standard string palindrome check.

Concepts Used in Above Programs

String Methods

  • split(), reverse(), and join() are key methods for reversing strings.

Number to String Conversion

  • The toString() method is used to convert numbers to strings for processing.

Case Normalization

  • The toLowerCase() method ensures consistent comparisons by normalizing the case of characters.

Spread Operator

  • The spread operator (...) provides a shorthand for converting a string to an array.

For Loop

  • Used for character-by-character comparison to check for mismatches.