Cool prototype patching

memoize.js

function memoize(fun) {
  // memoize a function with arbitrary arguments
  var memo = {}
  var name = fun.name || "anonymous";
  return function memoize_fun() {
    this.name = this.name + "__" + name;
    var args = arguments;
    var sargs = JSON.stringify(args);
    if (memo[sargs]) {
      return memo[sargs];
    }
    memo[sargs] = fun.apply(this, args);
    return memo[sargs];
  }
}

function time(fun) {
  // memoize a function with arbitrary arguments
  var name = fun.name || "anonymous";
  var now = new Date();
  return function() {
    var args = arguments;
    var res = fun.apply(this, args);
    console.log("[" + name + "] excecution time: " + (new Date() - now) + "ms");
    return res;
  }
}

var fib = function(x) {
  // you need an object so that you call the monkey-patched function
  return x <= 1 ? x : fib(x - 1) + fib(x - 2);
}

console.log("fib (42): " + time(fib)(42))
var fib = memoize(fib);
console.log("memoize(fib)(42): " + time(fib)(42));