Factorial using recursion

factorial.js

/* -------------------------------------------------------------------------- *\
 *  Utils
\* -------------------------------------------------------------------------- */

const isFunction = val => typeof val === 'function'

/**
 * Trampoline
 */
const T = fn => (...args) => {
  let result = fn(...args)
 
  while (isFunction(result)) {
    result = result()
  }

  return result
}



/* -------------------------------------------------------------------------- *\
 *  Factorial
\* -------------------------------------------------------------------------- */

/**
 * Recursive Solution
 * @example
 *   factorial(5)
 *   5 * f(4)[ 4 * f(3)[ 3 * f(2)[ 2 * f(1)[ 1 ]]]]
 *   5 * f(4)[ 4 * f(3)[ 3 * f(2)[ 2 * 1]]]
 *   5 * f(4)[ 4 * f(3)[ 3 * 2]]
 *   5 * f(4)[ 4 * 6]
 *   5 * 24
 *   = 120
 */
const simpleFactorial = function factorial(n) {
  if (n <= 1) return 1

  return n * factorial(n - 1)
}

/**
 * Tail call Optimized Recursive solution
 * 
 * Left to Right multiplication
 * @example
 *   factorial(5)
 *   f(5, 4) -> f(20, 3) -> f(60, 2) -> f(120, 1) -> 120
 *   = 120
 */
const optimizedFactorial = x => (function factorial(acc = 1, n = x) {
  if (n <= 1) return acc

  return factorial(n * acc, n - 1)
})()

/**
 * Trampolined Recursive Solution for non Tail call optimized JS enviroments
 * 
 * Left to Right multiplication
 * @example
 *   factorial(5)
 *   f(5, 4) -> f(20, 3) -> f(60, 2) -> f(120, 1) -> 120
 *   = 120
 */
const trampolinedFactorial = x => T(function factorial(acc = 1, n = x) {
  if (n <= 1) return acc

  return () => factorial(n * acc, n - 1)
})()



/**
 * Test
 * Dont worry about exceeding maximum call stack in JS enviroment
 */
console.log(trampolinedFactorial(100800)) // -> Infinity