Greatest Common Divisor, recursive & iterative

gcd.js

// recursive
var gcd = function(a, b) {
    if ( ! b) {
        return a;
    }

    return gcd(b, a % b);
};

// iterative
function gcd(a,b) {
    if (a < 0) a = -a;
    if (b < 0) b = -b;
    if (b > a) {var temp = a; a = b; b = temp;}
    while (true) {
        a %= b;
        if (a == 0) return b;
        b %= a;
        if (b == 0) return a;
    }
}