I learned a new feature of JS today

fibbonacci.js

function fib() { if(!x()) return z(); return fib(x(), y(), z()); }
function x() { return fib.arguments[0] - 1; }
function y() { return fib.arguments[2] || 0; }
function z() { return (fib.arguments[1] || 0) + (fib.arguments[2] || 1); }
[fib(1), fib(2), fib(3), fib(4), fib(5), fib(6)].join(); // returns '1,1,2,3,5,8'