Javascript Interview Question: Reverse a Number

reverse-number.js

/*
  Reverse a number. 
*/

function reverseInt(num) {
  //Convert the num to a string, reverse the chars.
  const reversedStr = num.toString().split('').reverse().join('');
  
  //Convert back to an int, restore the sign (+ or -), return result as number.
  return parseInt(reversedStr) * Math.sign(num);
}

//Jest
test('It should reverse 123 to 321.', () => {
  expect(reverseInt(123)).toEqual(321);
});

test('It should reverse 120 to 21.', () => {
  expect(reverseInt(120)).toEqual(21);
});

test('It should reverse -150 to -51.', () => {
  expect(reverseInt(-150)).toEqual(-51);
});

//Try it.
console.log(reverseInt(25));