RosettaCodeData/Task/Fibonacci-sequence/JavaScript/fibonacci-sequence-5.js

var fib = (function(cache){
    return cache = cache || {}, function(n){
        if (cache[n]) return cache[n];
        else return cache[n] = n == 0 ? 0 : n < 0 ? -fib(-n)
            : n <= 2 ? 1 : fib(n-2) + fib(n-1);
    };
})();