JavaScript: compute by recursive function call with cache

cacheCompute.js

/*
 * Extract from <JavaScript: The Good Parts>
 * General routine with cache for recursive function invoking
 */
var cacheCompute = function(cache, compute){
  var shell = function(n){
    var result = cache[n];
    if(typeof result !== 'number'){
      result = compute(shell, n);
      cache[n] = result;
    }
    return result;
  };
  return shell;
}

var fibonacciInstance = cacheCompute([0, 1], function(shell, n){
  return shell(n-1) + shell(n-2);
});

/*
 * Compute fibonacci with cache
 */
var fibonacci = function(){
  var cache = [0, 1];
  var fib = function(n) {
    var result = cache[n];
    if(typeof result !== 'number'){
      result = fib(n-1) + fib(n-2);
      cache[n] = result;
    }
    return result;
  };
  return fib;
}();