Memoized Fibonacci

function memoizer(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); });