Function factorial

maths/factorial.ts:10–16

(num: number)

 * @example factorial(3) = 6
 */
export const factorial = (num: number): number => {
  if (num < 0 || !Number.isInteger(num)) {
    throw new Error('only natural numbers are supported')
  }

  return num === 0 ? 1 : num * factorial(num - 1)
}