js: recursive sum, avg, gcd, and lcm

recnumeric.js

function sum(n) {
	return n.length ? n[0] + sum(n.slice(1)) : 0;
}

function avg(n) {
	return sum(n) / n.length;
}

function gcd(n1, n2) {
	return n1 % n2 === 0 ? n2 : gcd(n2 % n1, n1);
}

function lcm(n1, n2) {
	return (n1 * n2) / gcd(n1, n2);
}