Day 4 – Palindrome Number in JavaScript Without Converting to String

🔥 Interview Series – Day 4

💡 Topic: How to check if a number is a palindrome without converting it to a string in JavaScript

✅ Problem Statement

Check whether a given number is a palindrome without converting it to a string.

A number is a palindrome if it reads the same backward as forward.

🧪 Examples:

121 → true

123 → false

1221 → true

-121 → false (negative numbers are not palindromes)

🧠 JavaScript Code (Math-Based Logic):

function isPalindromeNumber(num) {

  if (num < 0) return false;

  let original = num;

  let reversed = 0;

  while (num > 0) {

    reversed = reversed * 10 + (num % 10);

    num = Math.floor(num / 10);

  }

  return original === reversed;

}

💡 Tips to Remember:

Avoid using .toString() — focus on mathematical logic.

% (modulo) gives the last digit.

Math.floor() removes the last digit from the number.

Store the reversed number and compare it to the original.

🧑‍💻 Why Interviewers Ask This:

To test pure logic-building without shortcuts.

To see how well you manage numeric manipulation.

🧠 Alternate Approach (String Method):

function isPalindrome(num) {

  if (num < 0) return false;

  const str = num.toString();

  return str === str.split('').reverse().join('');

}

Use this only if allowed. Real interviews often ban built-in shortcuts!