Caching wrapper redux

gistfile1.txt

Function.prototype.cachify = function () {
  var cache = {}, self = this;
  return function (arg) {
    if (arg in cache) {
      console.info('cache hit');
      return cache[arg];
    }
    return cache[arg] = self.call(self, arg);
  };
};

isPrime = isPrime.cachify();
sin = Math.sin.cachify();

console.info(isPrime(3));
console.info(isPrime(3)); // cache hit
console.info(sin(60));
console.info(sin(60)); // cache hit