Recursive factorial

var factorial = function(n) {
	// base case: 
	if (n === 0){
	    return 1;
	}
	// recursive case:
	return n* factorial(n-1);
}; 

println("The value of 0! is " + factorial(0) + ".");
println("The value of 5! is " + factorial(5) + ".");

Program.assertEqual(factorial(0), 1);
Program.assertEqual(factorial(5), 120);
Program.assertEqual(factorial(7), 5040);
Program.assertEqual(factorial(3), 6);