reverseNumber.js

/**
  * @param {Number} n
  * @return {Number} 
  * @example
  *
  * reverseNumber(123)       // 321
  * reverseNumber(212)       // 212 
  * reverseNumber(123456789) // 987654321
  */
const reverseNumber = (input) => {
    let result = 0;

    while (input > 0) {
        const lastNum = input % 10;
        result = (result * 10) + lastNum;
        input = (input / 10) | 0; // parseInt
    }

    return result;
}