const reverseInt = int => {
  // convert the number to a string
  const toStr = int.toString()

  // reverse the string
  const strReversed = toStr.split("").reverse().join("")

  // convert the reversed string to a number
  const intReversed = Number.parseInt(strReversed, 10)

  // If int is positive, then return the number; otherwise, return the number multiplied by -1
  return intReversed * Math.sign(int)
}

console.log(reverseInt(514))
// 415

console.log(reverseInt(-500))
// -5

Number.parseInt()

Number.parseInt(string, radix)

The Number.parseInt() method parses a string argument and returns an integer of the specified radix (base).

radix

Any number system with radix (or base), r consists of 0 to r-1 symbol to represent any number. For example, decimal number system having radix, r-10, uses 0 to 9 numbers.

If radix is undefined or 0, it is assumed to be 10.

// radix is assumed to be 10
const num = Number.parseInt("340")

console.log(num)
// 340

console.log(typeof num)
// number

Math.sign()

The Math.sign() function returns 1 if the argument is positive, -1 if the argument is negative, 0 if the argument is positive zero, -0 if the argument is negative zero, NaN if otherwise.

console.log(Math.sign(2))
//  1

console.log(Math.sign(-5))
//  -1

console.log(Math.sign(0))
//  0

console.log(Math.sign(-0))
//  -0

Learn how to reverse a string in my blog post here.