Palindrome numbers in JavaScript

We are required to write a JavaScript function that takes in a number and determines whether or not it is a palindrome number.

Palindrome numbers ? A palindrome number is that number which reads the same from both left and right sides.

For example ?

• 343 is a palindrome number

• 6789876 is a palindrome number

• 456764 is not a palindrome number

Method 1: String Reversal Approach

The simplest approach is to convert the number to a string, reverse it, and compare with the original:

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

console.log(isPalindromeString(343));      // true
console.log(isPalindromeString(6789876));  // true
console.log(isPalindromeString(456764));   // false

true
true
false

Method 2: Mathematical Approach

For a pure mathematical solution without string conversion:

const isPalindrome = num => {
    let length = Math.floor(Math.log(num) / Math.log(10) + 1);
    while(length > 0) {
        let last = Math.abs(num - Math.floor(num/10)*10);
        let first = Math.floor(num / Math.pow(10, length - 1));
        if(first != last){
            return false;
        };
        num -= Math.pow(10, length-1) * first;
        num = Math.floor(num/10);
        length -= 2;
    };
    return true;
};

console.log(isPalindrome(343));      // true
console.log(isPalindrome(6789876));  // true
console.log(isPalindrome(456764));   // false

true
true
false

Method 3: Reverse and Compare

Another mathematical approach that reverses the entire number:

const isPalindromeReverse = num => {
    const original = num;
    let reversed = 0;
    
    while (num > 0) {
        reversed = reversed * 10 + num % 10;
        num = Math.floor(num / 10);
    }
    
    return original === reversed;
};

console.log(isPalindromeReverse(343));      // true
console.log(isPalindromeReverse(6789876));  // true
console.log(isPalindromeReverse(456764));   // false

true
true
false

Comparison

Conclusion

The string reversal method is the most readable and intuitive for checking palindrome numbers. For performance-critical applications, use the mathematical approaches to avoid string conversion overhead.