# Factorial of number

Calculates the factorial of a number.

- Use recursion.
- If
`n`

is less than or equal to`1`

, return`1`

. - Otherwise, return the product of
`n`

and the factorial of`n - 1`

. - Throw a
`TypeError`

if`n`

is a negative number.

const factorial = n => n < 0 ? (() => { throw new TypeError('Negative numbers are not allowed!'); })() : n <= 1 ? 1 : n * factorial(n - 1); factorial(6); // 720