factorial

factorial.js

function factorial (n) {
	return n <= 1 ? 1 : n * factorial(n - 1);
};

var factorial_memo = (function () {
	var memo = [1];
	function fac (n) {
		var result = memo[n];
		if (typeof result !== 'number') {
			result = n * fac(n - 1);
			memo[n] = result;
		}
		return result;
	};
	return fac;
}());

for (var i = 0; i <= 40; i += 1) {
	console.log('// ' + i + ': ' + factorial(i));
}

for (var i = 0; i <= 40; i += 1) {
	console.log('// ' + i + ': ' + factorial_memo(i));
}