Bypassing stack-overflow through trampolining. See: <https://groups.google.com/group/jsmentors/browse_thread/thread/ac6f4a0e6cbb67a0?hl=en>

fibTrampoline.js

function trampoline(f) {
    while (typeof f === "function") f = f();
    return f;
}

function fib(n){
    function f(n0,n1,step){
        return step == n ? n1 : function() { return f(n1, n0 + n1, step +1) }
    }
    return trampoline(f(0,1,1))

}