cached prototype using clousure

cached-prototype.js

Function.prototype.cached = function() {
   var self = this, //"this" refers to the original function
      cache = {}; //our local, lexically scoped cache storage
   return function(args) {
      if(args in cache) return cache[args];
      return cache[args] = self(args);
   };
};

Math.sin = Math.sin.cached();
Math.sin(1) // => 0.8414709848078965
Math.sin(1) // => 0.8414709848078965 this time pulled from cache