math

factorial.js

function factorial(n) {
    if (n < 2) {
        return 1;
    }
    return n * factorial(n - 1);
}

fibo.js

/*
first   : first number of sequence
second  : second number of sequence
max     : the number sequence must stop before
*/
function fib(first, second, max) {
    if (second < max) {
        console.log(first);
        console.log(second);
        fib(first + second, second + second + first, max);
    }
}