/*
author: PatOnTheBack
license: GPL-3.0 or later
Modified from:
https://github.com/TheAlgorithms/Python/blob/master/maths/factorial_python.py
This script will find the factorial of a number provided by the user.
More about factorials:
https://en.wikipedia.org/wiki/factorial
*/
'use strict'
const calcRange = (num) => {
return [...Array(num).keys()].map((i) => i + 1)
}
const calcFactorial = (num) => {
if (num === 0) {
return 1
}
if (num < 0) {
throw Error('Sorry, factorial does not exist for negative numbers.')
}
if (!num) {
throw Error(
'Sorry, factorial does not exist for null or undefined numbers.'
)
}
if (num > 0) {
const range = calcRange(num)
const factorial = range.reduce((a, c) => a * c, 1)
return factorial
}
}
export { calcFactorial }