Reverse_number.js

function reverseInteger(input) {
  let number = Math.abs(input); // holds a new copy of the absolute value of the input integer
  let result = 0; // creates a result variable to hold the aggrigate of our while loop
  
  while (number > 0) { // while the number is greater than 0 (simplified way of saying less than or equal to 1)
    const lastDigit = number % 10; // each iteration runs modulo 10 on the number variable giving us the last digit
    result = result * 10 + lastDigit; // sets result equal to itself multiplied by 10 plus the last digit 
    number = Math.floor(number / 10); // removes the last number for the next iteration
  }
  
  const sign = input < 0 ? -1 : 1; // creates a variable either 1 or -1 depending on input numbers quality
  return result * sign; // returns the result with the appropriate input quality (+ or -)
}

Add the code for reverse number.
For ex:) input number is 123 -> result is 321

Reverse_String is more simple.

const reversedString = str.split('').reverse().join('');