Douglas Crockford's memoizer

gistfile1.js

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

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