Two ways to calculate factorials: recursively and iteratively. http://jsperf.com/recursive-vs-iterative-factorial

factRecursiveAndIterative.js

// recursive
var factorial = function(n) {
    if (n == 1) {
        return 1;
    } else {
        return n * factorial(n-1);
    }
}

// iterative
var factorial = function(n) {
    for (i=n-1;i>=1;i--) {
        n*=i;
    }
    return n;
}