Computing the factorial in JavaScript.

factorial.js

/**
 * Computes the factorial of a given non-negative integer using iterative solution.
 * @param {number} n The positive integer.
 * @return {number} Returns a factorial of 'n'.
 * @see https://en.wikipedia.org/wiki/Factorial
 */
function factorial(n) {
  var result = 1;

  for (var i = 1; i <= n; ++i) {
    result *= i;
  }

  return result;
}


/**
 * Computes the factorial of a given non-negative integer using `while` loop in reverse.
 * @param {number} n The positive integer.
 * @return {number} Returns a factorial of 'n'.
 * @see https://en.wikipedia.org/wiki/Factorial
 */
function factorial(n) {
  var result = 1;

  while (0 < n) {
    result *= n--;
  }

  return result;
}


/**
 * Computes the factorial of a given non-negative integer using recursive solution.
 * @param {number} n The positive integer.
 * @return {number} Returns a factorial of 'n'.
 * @see https://en.wikipedia.org/wiki/Factorial
 */
function factorial(n) {
  return 2 > n ? 1 : n * factorial(n - 1);
}