Euler Problem 5 in JavaScript

euler5.js

// Euclidean Algorithm
function gcd(a,b) { while (b) { var t = b; b = a%b; a = t } return a }

function lcm() { return Array.prototype.reduce.call(arguments, function(a,b){ return (a*b)/gcd(a,b) }) }

// http://projecteuler.net/problem=5
// lcm(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,1,18,19,20)
// but we only need... ehm... primes but from last to first?
lcm(20, 19, 18, 17, 16, 15, 14, 13, 12, 11)