Various JavaScript implementations of a generator for the Fibonacci numbers.

fibs.js

// Naive -> fib(30) runs 2692537 times
var fibNaive = function(num) {
    if (num === 0) return 0;
    if (num === 1) return 1;
    return fibNaive(num - 1) + fibNaive(num - 2);
}

// Memoized -> fib(30) runs 59 times
var memo = {};
var fibMemo = function(num) {
    var result;
    if (typeof memo[num] !== 'undefined')
        return memo[num];    
    else if (num === 0)
        result = 0;   
    else
        if (num === 1) result = 1;
    else
        result = fibMemo(num - 1) + fibMemo(num - 2);
    memo[num] = result;
    return result;
}

// Iterative -> fib(30) iterates 29 times
var fibIter = function(num) {
    var prev1 = 1, prev2 = 0;
    var current = 0;
    for (var n = 2; n <= num; n++) {
        current = prev1 + prev2;
        prev2 = prev1;
        prev1 = current;
    }
    return current;
}