gen_memo.js

var memoizer = function (memo, fundamental) {
    var shell = function (n) {
        var result = memo[n];
        if (typeof result !== 'number') {
            result = fundamental(shell, n);
            memo[n] = result;
        }
        return result;
    };
    return shell;
};

//usage example
var fibonacci = memoizer([0, 1], function (shell, n) {
    return shell(n - 1) + shell(n - 2);
});