Factorial with memoization

factorial.js

var factorial = (function () {
  var cache = [1];

  return function factorial(n) {
    if(n < 0) {
      return Infinity;
    }
    n = parseInt(n);
    if (n < cache.length) {
      return cache[n];
    }
    for (var i = cache.length; i <= n; i++) {
      cache[i] = i * cache[i - 1];
    }
    return cache[n];
  }
})();